I've just published my first payed application, but very cheap ($1). It is an application that replaces the huge calendar widget on your home screen by a notification on the status bar, where you can get detailed information about upcoming events. Also, it allows you to monitor changes on calendars, so you can share a calendar with a friend and whenever plans change, you'll be notified of that change and what was changed. You can even put information about the location and description and that will show up on the event information a click away (great to not send SMS or emails).
I use it to coordinate with my family and friends, I just thought I might as well share this new functionality to the rest of the world.
Suggestions and bug reports are more than welcome