When comparing WAVE calendar vs QKSMS, the Slant community recommends QKSMS for most people. In the question“What are the best Material Design apps?” QKSMS is ranked 7th while WAVE calendar is ranked 28th. The most important reason people chose QKSMS is:
When a new sms is received, a window will pop up that has the message and allows answering it from there, without having to open the app. It can be dismissed by tapping anywhere else on the screen.
Specs
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Pros
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.
Pro Allows responding to SMS without opening the app
When a new sms is received, a window will pop up that has the message and allows answering it from there, without having to open the app. It can be dismissed by tapping anywhere else on the screen.

Pro Per-conversation notification settings
Users can set different notification settings per user as an easy way to know who is messaging without having to look at the actual message.

Pro Easily communicate with groups
Users can communicate with large groups at the same time due to the included group messaging feature. This is convenient when trying to synchronize with friends or colleagues.
Pro Very active developer who listens to the community
While QKSMS is one of the younger apps, the developer is quickly adding features/fixing bugs.
Pro Free
The app is available for free with an optional donation IAP that ranges from $1-$10.
Pro Beautiful design
Responsive, highly customizable Material Design interface makes for a native looking app that fits in well with Google's UI design guidelines.

Pro Save yourself from sending out bad messages
Through delayed messaging one can set it up so that a message is not sent automatically. This can help for those times that it may be best to think something over before sending out a rash message.
Pro Readable in day or night due to themes
There are light and dark themes available within the settings which can be switched depending on how light it is around one when using the app. The dark theme can also help to conserve battery when being used as not as much brightness and hence battery will be used.
Pro Schedule messages
Users can schedule messages to be sent for later.

Pro Convenient Android Wear support
Those that own an Android Wear device will be able to set it to receive their messages on the Android Wear device making for convenient notifications and easy messaging through not having to take their phone out.
Cons
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
Con Last update was 2021
Con Buggy
There are little annoyances here and there, from dark theme problems making text unreadable to crashing and missing notifications.
Con Lacks features compared to other offerings
