I hacked up a Twitter clone which works on the micro-browser of Polycom phones on the weekend.
One annoying part of the microbrowser in Polycom phones is that it re-posts forms without any requested confirmation... so the 'Back' button would cause a repost. I fixed that by implementing a quick cookie.
One motivation in writing the app was working with the no-SQL database Redis. The best description for Redis is memcached+disk storage. It also has some unique features sets and lists.
It's really a great way to hack and test out some code as you can just start up the Redis server, import the client library and go. There no need to think too hard about schema (XML feels like this too).... It feels like a natural extension from the programmatic datatypes that you are accustomed to hacking with.
Working with a no-SQL database also makes you think differently. You find yourself thinking less about the potential impact/overhead you would have on a database if you performed a particular operation. Again that leads to more hacking fun as you just quit to the chase and hack away at your brand new persistent storage friend.