I released the source code to my Danger Hiptop / T-Mobile Sidekick apps from 2003-2005. Because of the early date, many of these apps are the first of their kind.
One app, Tower Power, lets you find nearby restaurants and list them on a map.
Another, Flipper, lets you message your friends directly, send the photos, query their location, and share appointments -- like Avocado, Couple, and iMessage.
Flipsheet is a spreadsheet program and my request to Danger to let me handle CSV attachments in Email messages was one inspiration for the Intent registration system in Hiptop OS, which also appears in Android!
Here's the source code, screenshots, a few links to blog articles back in the day, and other commentary:http://hipme.com
Thanks to Facebook post https://www.facebook.com/s4xton
for getting me to do this.
And apologies to +Andy Rubin
and +Brian Swetland
and others from Danger if my inclusion of my hacked-up copy of the Hiptop OS scroller widget in Flipsheet is a problem.