When comparing Google Calendar vs Slack, the Slant community recommends Google Calendar for most people. In the question“What are the best Material Design apps?” Google Calendar is ranked 1st while Slack is ranked 13th. The most important reason people chose Google Calendar is:
Google Calendar has a monochrome base design that's accented with colored-coded events and image banners that separate months in schedule view. The app has 5 different views - schedule, day, 3-day, week and month. Day, 3-day and week views split up the days horizontally and hours vertically. Month view lays out all days in a grid and displays up to 3 events in a day. Schedule view displays an agenda view that allows browsing all events by swiping vertically. Additionally, the way events are displayed in the agenda view is context-aware. For example, adding an event called "gym" will display the event on a background with a dumbbell. All views except for month view can be split horizontally to display a condensed month view at the top that can be navigated by swiping horizontally. Events can be added from any view by clicking the red plus button that's available at the bottom-right corner of the screen.
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Pro Clean design with 5 different views including an excellent schedule view
Google Calendar has a monochrome base design that's accented with colored-coded events and image banners that separate months in schedule view.
The app has 5 different views - schedule, day, 3-day, week and month.
Day, 3-day and week views split up the days horizontally and hours vertically. Month view lays out all days in a grid and displays up to 3 events in a day.
Schedule view displays an agenda view that allows browsing all events by swiping vertically. Additionally, the way events are displayed in the agenda view is context-aware. For example, adding an event called "gym" will display the event on a background with a dumbbell.
All views except for month view can be split horizontally to display a condensed month view at the top that can be navigated by swiping horizontally.
Events can be added from any view by clicking the red plus button that's available at the bottom-right corner of the screen.
Pro Integrates well with other Google services
Google Calendar is part of the Google ecosystem, it integrates with services like Google Now for creating events, Google Maps for directions and Gmail for pulling information about planned flights.
Pro Integrates with Google Maps for directions
The app leverages Google Maps when adding location for an event by offering suggestions as well as offers opening Maps to help get directions to an event via shortcut on a reminder notification.
Pro Comes pre-installed on most Android devices
Google Calendar is a free Android calendar app without ads that comes already installed on Android devices that have stock support for Google Services.
Pro Offers creating events from e-mail messages based on content
Google Calendar integrates with e-mail for quickly creating events from e-mails that contain the word "meeting" or dates or times, or any other information about events or plans that it can understand.
Pro Can set on-screen and e-mail reminder notifications
Google calendar allows setting how many reminders are needed with each having the ability to set how long before the event the notification should remind and if it should be done via on-screen or e-mail notification.
Pro Straightforward event creation with autocomplete
All views have an option of adding a new event by tapping the plus sign at the lower right corner of the screen. This opens up a form and allows the user to add a location, start/end times, guests, description, color-code as well as choosing if it's an all day event, how often it repeats, how many and what kind of reminders are needed and setting the users availability and privacy settings.
Pro Color-coding for events and calendars
The app will color-code different calendars in different colors as well as allow selecting a different color for each event.
Pro Supports non-Google calendars (requires accessing web client)
Google Calendar can be integrated with any calendar that support iCalendar format, including Exchange and iCloud, via URL, but it has to be done using the web client.
Pro Lots of third-party widgets
Google Calendar comes with a home screen widget, and there are also many third party widgets developed for this calendar app.
Pro Allows subscribing to public calendars through web client
Through the Google Calendar's web client, it is possible to subscribe to any public calendar. Google also maintains a list of public calendars for various sports events and holidays in different countries and for different religions.
Pro Advanced functionality available through IFTTT
IFTTT offers over 198 channels to plug into the users Google Calendar.
Pro Awesome flairs / images view inside the agenda view / event page
Whenever you enter agenda / event title with the keywords (when available), the event will show up interesting flairs whenever the keyword inside the agenda / title you typed matches the flairs that are available inside the system, examples such as haircut, cycling, swimming, coffee, movie etc.
Pro Robust integration with a huge number of tools
Slack integrates with tools like Trello, GitHub, Dropbox, Mailchimp, and dozens of others, so you can have a centralized event feed of your project right alongside your chat. This is tremendously useful for keeping context with your discussions.
Pro Drag & drop files in channels
You can upload a file to any channel over HTTPS simply by dragging and dropping.
You can ping people to get their attention even if they are not online by @mentioning them. Slack supports desktop notifications.
Pro Fantastic search functionality
You can deep search messages, files and snippets. Given Slacks integration into many external services, Slack is good enough to act as the central search interface for your entire team.
Pro Very polished user experience
The entire Slack interface is polished and intuitive to use. There are very few bugs or inconsistencies in the UI and it's very fast to use. There is nothing in particular that is new with Slacks implementation of team chat, but the execution of the groups (called channels), search, external service integration and notifications is close to perfect.
Pro Apps for iOS, Android, Windows Phone, Mac OS, Linux, and Windows
Slack has apps for iOS, Android, Windows Phone, Mac OS, Linux, and Windows to give you the full functionality of Slack with some extra features not found on the website on most major platforms.
Pro Supports multiple teams
You can be signed into multiple teams simultaneously and quickly switch between them.
Pro Flexible, granular notification settings
Notifications are handled separately for mobile and the web app. You can receive notifications for all messages, just direct messages, or based on filters, and you can have different settings for different channels: you don't have to get notified every time someone pushed to GitHub or every time someone posts to off-topic chat, unless you want to.
Pro Freemium plan
Free forever, only restriction on searchable message archives, up to 10k of your team’s most recent messages and 10 apps or service integration. Great for trying out first
Pro Slackbot extensible chat robot
The "Slackbot" can is an extensible robot that can be set you remind you about tasks, auto respond to certain phrases and a variety of other functionality.
Pro Syntax coloring
Pasted code can be colored based on syntax.
Pro Inline link previews (photos, mockups, etc.)
When a link is added, some content in the link is shown such as image - like how Facebook does it when you share a link.
Pro Edit messages easily
It allows you to change what you sent by hovering to the message and selecting "Edit message" under the ellipsis (...).
Pro Emoji reactions to limit excessive posts and notifications
Pro Shows local time of each participant
You can click on the profile of a user to see their local time. An especially useful feature when members of your team are working in different timezones.
Pro Dev team is invested, responsive, and friendly
Having submitted both feedback and support requests for bot development, I can personally attest that the team takes feedback seriously, and responds quickly to communication. This is vital for any closed-source or hosted project.
Pro IRC connectivity over SSL
Pro Self chatting
Creative implementation which is very good for personal journaling or drafting/collecting ideas. Previously, to do this, users needed to create a private channel with themselves. Note that some other team-chat apps may disallow creating group/channel with no 2nd person(s).
Pro It can surprise you
There's a checkbox in preferences under advanced options that may surprise you.
Pro Multiple channels for different groups
Con No weather forecast
The Android app version of Google Calendar does not show any weather forcast information, even if it is added as an extra calendar in the web application. Being that weather is tied into Google Now, the absence is surprising.
Con Privacy concerns
Google integrate all their services to connect and mine information on an individual to better profile and target advertising.
Con Google tasks do not show on Google Calendar
You can create tasks in your desktop Google Calendar but they will not sync nor show up in your android Google Calendar
Con Month view shows limited information about the event
Month view does not show how many events there are in each given day or color-code them in any way, only informs of their existence.
Con Weak default view
Even if month is set as default view, as soon as you touch a day or an event, you have to carefully select twice to get back to month view.
Con Time zone is incorrect no matter what's done
Con Timezone for Moscow is incorrect
Timezone for Moscow is 1 hour off. This makes the calendar unusable in Russia.
Con No natural language input support
The Android app has no natural language input support, while it's available using the web client and in a limited capacity using Google Now.
Con Setting up non-Google calendars requires accessing web client
There is no ability in the Android app to access other calendars. This limits the usefulness for people that use more than one calendar, such as OSX and iOS users.
Con Expensive when you need to upgrade
At $6.67 per user / month (or $8 if billed monthly) , Slack is significantly more expensive than the competition if you need features such as unlimited integrations (more than 10) or unlimited message storage (more than 10,000). However, the free version of Slack includes unlimited users.
However if you need only unlimited messages you can use storage services like https://slarck.com to upload then browse and search your entire message history, while staying in Slack's free plan. So with a combo of Slack+Slarck this con is not that major.
Con No self-hosting available
If you are worried about third-parties getting access to your data you should consider self-hosting. With self-hosting you are in control over where your data is stored, who has access to it. You will also not be vulnerable to exploits of a third-party provider.
Con Hidden max limit of free users per channel
Slack says that their free accounts support an unlimited number of users, which is true. However they don't mention that there is an undisclosed maximum number of users per channel (8462). For a large open source community, this is something to keep in mind.
Con Proprietary (non-free/libre)
Con Linux client is very RAM intensive
Con "Native" desktop apps are web apps
While it's great that Slack provides installable apps for Windows, macOS, and Linux, they're just the Slack web app wrapped in Electron shell. This means they don't offer the same level of native UX that a truly native toolkit app would.
Con Slow and lags sometimes
Con API doesn't allow custom widgets in chat
Con Awful performance and constant glitches, since it is Chromium-based
You will experience a lot of hangs and glitches and it eats immense (for as basic as UI is) amount of RAM.
Con API is overall very poor
Can't do much with integrations.
Con No E2E encryption
Data is sent of SSL only, not E2E encrypted.