When comparing WhatsApp vs WAVE calendar, the Slant community recommends WAVE calendar for most people. In the question“What are the best Material Design apps?” WAVE calendar is ranked 28th while WhatsApp is ranked 34th. The most important reason people chose WAVE calendar is:
Available in English, Dutch, Spanish, Swedish, Italian, Portuguese, German, Chinese, and Russian.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Straightforward interface
The interface is very simple, fast and easy to use. You can start using it as soon as the app has been downloaded - it does not require setting anything up or registering. You can communicate with anyone in your contacts list that also uses WhatsApp. Includes useful features like seeing when a contact is currently available or typing.
Pro Widely used
WhatsApp reported 1.5 billion users in 2018. Your friends are most likely already using WhatsApp, so it's easy to get setup.
Pro Effortlessly builds your contacts by using your phone number as identification
WhatsApp will automatically find all of your contacts currently using Whatsapp and add them to your contacts. This makes it really easy to setup and given that it's the most popular messaging app it's likely that a lot of your contacts are already using it.
Pro Message mirroring on web app
WhatsApp can be used from the desktop via Chrome, Firefox and Opera browsers. Accessing it requires using the Android app to scan the QR code that's presented on web.whatsapp.com.
Pro Signal protocol
Whatsapp uses the state-of-the-art Signal protocol that ensure strong end-to-end encryption.
Pro One-on-one texts can be encrypted
WhatsApp has implemented end to end encryption for messages sent on it's service. Even WhatsApp has no way to read a users messages.
Pro Available in 10 languages
Available in English, Dutch, Spanish, Swedish, Italian, Portuguese, German, Chinese, and Russian.
Pro Integrates with Google Maps for directions
If a location to an event is added, the app will show a map and allow pulling up Google Maps for directions.
Pro Built-in task manager that can integrates with Google Tasks
Wave allows creating local and Google Tasks to-do items that can be synced across devices and color-coded.
Pro Has day and week, month, list and 2 agenda views
The app has day, week, week-agenda, month, month-agenda and list views.
Day, 3-day and week views split up the days horizontally and hours vertically.
Week agenda splits the screen in 6 equal parts - 5 parts for work days, sixth for weekend. Double-tapping a day will open a list of events for that day. From here swiping left and right allows moving between days.
Month view splits the screen in half with one half displaying a typical month view with color-coded dots next to dates to show which days have events and the other a list of events for the selected day.
Month agenda view lays out all days in a grid and displays all event for the day.
The list view is actually the closest to a typical agenda view despite the name. The difference here is that there are two modes of showing that information - default and detailed. The default mode displays date, time, event name and location (if available) and the detailed mode displays extra information such as what calendar is the event part of, who's attending, notes, etc.
Pro Integrates with Wave Scheduler for event planning
Another app on offer from the publisher is WAVE Scheduler, which integrates into WAVE Calendar for easy event planning.
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 Includes a store for purchasing various public calendars
The app has a store for sports, stock exchange, holiday, religion and other calendars.
Cons
Con Shares meta data with Facebook
WhatsApp shares your messaging meta data with Facebook if you do not opt-out in the settings. If you use the same phone number for WhatsApp and Facebook, the profiles can easily be linked.
See https://www.whatsapp.com/faq/en/general/26000016
Con Tied to carrier phone number
WhatsApp cannot be used by people without a smart phone with an active cell plan. If your phone is lost or damaged, or if your phone number changes, you cannot get messages sent by friends without them updating your phone number. You cannot send message to them until you are able to get SMS messages at your phone number.

Con Proprietary
Not open source.
Con Hard to migrate history cross platform
Migrating your chat history from Android to iOS or the other way around is not so simple. In some cases it requires a 3rd party app and in some the only way is to migrate specific chats one by one.
Con Web interface uses message mirroring
To use your computer to send messages your phone must be on with a consistent data connection.
Con Single device
You cannot use the same WhatsApp account on multiple devices (e.g. a tablet, a PC and a cellphone). The account is tied to the device with the specific cellphone number. Chat history is deleted when you sign in to a new account, unless you have created a backup.
Con No cloud sync
Messages are not stored on WhatsApp server for privacy and security reasons.
Con Limitation on shareable file sizes
WhatsApp now allows users to share files of any type, but there is still a 16 MB size limit.
Con Some basic features require signing up
Paid features include the ability to add attachments and travel time to events and see local weather in calendar.
Con Inconsistent design
There's different branding in different places (Still has e-cal branding in some places). Sometimes looking at an event requires tapping twice while most of the time it's once, a horizontal list of items looks differently based on the views it's accessed through, etc.
Con No natural language input support
