When comparing Trello vs Slack, the Slant community recommends Slack for most people. In the question“What are the most useful collaboration tools for remote teams?” Slack is ranked 1st while Trello is ranked 3rd. The most important reason people chose Slack is:
You can upload a file to any channel over HTTPS simply by dragging and dropping.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Simple and easy to use interface
There are two primary columns: the board is shown on the left and all the other controls on the right. The main means of interaction is dragging and dropping to-do cards into the various lists.
The board structure is very customizable, and includes a variety of features that help along the way: color-coding, due dates, card images, checklists with a graphics bar that allows following progress easily, and card aging for cards that haven’t been touched in a long time.
Pro Great real-time team collaboration features
Trello has permissions at the board level as well as the ability to assign multiple people to each card. There are a lot of sharing options available and boards can be made visible for the public. It's also possible to subscribe to a card to be notified of its progress. The simplicity of the UI makes collaboration easy because it’s very simple to see the progress of each card and who is responsible for it. It also updates constantly to reflect real-time changes in progress.
The simplicity of the UI makes collaboration easy as it’s very simple to see the progress of each card and who is responsible for it. It also reflect changes on boards in real-time.
Pro Highly flexible workflow
Trello calls items used in the workflow “cards.” Cards are double-sided and can contain subtasks as well as notes and other details.
Card columns can be used to simulate a workflow by moving cards from left to right as they are completed, or as a way of indicating task priority.
The workflow is highly flexible as the columns are completely customizable to suit the task flow. For example, tasks can be put through a workflow "idea > approved > in-progress > pending review > released" or simply "ideas > released" depending on the granularity level needed.
This makes Trello a great solution to feature management as it's possible to set up boards to handle everything from agile sprints to a more generic to-do list, all with status management.
Pro Free for unlimited users
Trello offers a very generous free version that has no ads, no restrictions on the number of users, and very little restriction on how the program can be used. The paid features are generally cosmetic, such as the ability to change the background, add stickers or integration with other tools.
Pro Works well for visual thinkers
The UI is based around Kanban, so you can see all your tasks and their status clearly.
Pro Functionality can be extended via plug-ins
Voting, view, and calendar plug-ins further increase the functionality.
Pro Markdown support with well-rendered images
Trello supports Markdown, meaning that HTML input is represented appropriately. Cards with attachments are also rendered well. For example, images are shown correctly on the card, bug links are detected etc.
Pro Sub-tasks
Each card can have one or even multiple task lists.
Pro Cross-platform and cross-sync
Trello works on all modern devices through the web application and has native apps for iOS, Android and Windows 8/10 devices.
Pro Attach files to cards
Keep all of your files (images, documents, etc.) organized on their relevant cards.
Pro Easy-to-use
Pro Best kanban for personal usage
Pro Excellent for groups using agile software development
The responsiveness and layers of customization make it easy for team members of various disciplines to collaborate on the same task board.
Pro Great prioritization, Due date and Story point features
Can set different priorities to various tasks, set appropriate due dates and Story points - timing allotted to each task.
Pro Good performance
Pro Features to add voting on cards
Trello offers support for features to add voting on cards, often referred to as 'power-ups'.
Pro Smooth media integration
Works like a charm.
Pro Great native app for Android and iOS
Pro Lots of API integrations
Pro Action history log allows you to rapidly follow changes
There is a global history system which allows to rapidly follow changes. There is also a notification system if another user updates the board while you're watching it.
Pro Drag & drop files in channels
You can upload a file to any channel over HTTPS simply by dragging and dropping.
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 @mentions
You can ping people to get their attention even if they are not online by @mentioning them. Slack supports desktop notifications.
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 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 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 Emoji reactions to limit excessive posts and notifications
Pro Multiple channels for different groups
Pro Syntax coloring
Pasted code can be colored based on syntax.
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 GIFS
easily embed gifs with /giphy
slash command.
Pro IRC connectivity over SSL
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 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 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 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 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 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 Can Create Diagrams with Creately
You can just create flowcharts, org chart, mind maps, UML charts, infographics and many more by typing /creately new <document name>
Pro It can surprise you
There's a checkbox in preferences under advanced options that may surprise you.
Cons
Con Subtasks lack features
Every task can have a list of subtasks which more closely resembles a standard to-do list.
These lack the functions that cards offer you. You cannot comment on a sub-list, give the sub-tasks due dates, or provide additional information. You are limited to only checking them off once completed.
Con No multi-board aggregation
If you have multiple boards with tasks on them there is no way to get all the tasks on one board in a way that changes on one board will update the other.
Con Can't get one view of cards across all boards
However, you can view all cards assigned to you.
Con Not really a to do list
Trello is much more a workflow and project management program than a typical to-do app, which makes it overwhelmingly robust for those looking to jot down their shopping list.
Con You can't add more than 1 Power Up without paying for it
Con Can't create dependencies between cards
Con Project management system only
This is cumbersome to get started.
Con Managing large projects may be difficult
Trello works best with medium to small projects and with very high-level overviews. It is less effective for projects that require very granular management due to the fact that it becomes considerably more difficult to keep track of various cards and priorities as they are pushed off the screen.
Con Impossible to use Pomodoro timer connected to Trello on iOS
Con No quick deadline assignment
You have to open a Calendar every time to set a date without any quick options like today, tomorrow etc.
Con Slow and requires a lot of mouse work to navigate
Con Light on features
Trello is focused on simplicity and as such forgoes certain common features that may or may not be important to you.
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 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 Slow and lags sometimes
Con No E2E encryption
Data is sent of SSL only, not E2E encrypted.
Con API doesn't allow custom widgets in chat
Con API is overall very poor
Can't do much with integrations.
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.