CalWatch was a fun project that I built to teach myself how Android and Android Wear work together and to solve the problem of quickly telling time and knowing my availability. It works on any Android Wear device and compatible Android phone (Android 4.4 "KitKat" or later), reading your calendar on the phone and sending the relevant parts to your watch.
Here's a Google Play Store link. It's free to download and install on your personal device.
CalWatch, by design, needs to read your calendar. It does nothing else with it except to display your free/busy time to you. CalWatch will not transmit your personal information to anybody, at all, ever. If CalWatch crashes, you'll have the option to send debugging information back to help me fix the problem. Your calendar data will not be part of this.
I wrote a one-hour lecture to introduce Android development to my college sophomore-level CS class, using CalWatch as a running example. This lecture assumes you already know how to program Java.
If you read the lecture slides, then you'll probably want to read along with the code. I'm providing everything you need on Github as a public project, this includes the complete revision history, so if you're really into it, you can see something of the software engineering process in action.
I've decided to release this under a "dual" license. This means that developers are free to read the code and create derived works, while publishing their changes; commercial developers may contact me if they're interested in other options.