These apps were built with the Garmin Connect IQ SDK. The SDK can be downloaded from here: developer.garmin.com/connect-iq/sdk/
They are written in Monkey C
and were developed with the Eclipse IDE
The API is documented here: developer.garmin.com/connect-iq/api-docs/
Garmin Connect IQ Apps for your wearable can be found in the store
Do you have an idea for a new app? Send me an email, I'll look into building it for you.