BREADBOX64 is a twitter client for the C64/128 which allows you to tweet from a real C64 and show your friends timeline. It uses Contiki, a very nice embedded OS, and the MMC Replay cartridge with the RR-Net add on for the physical connection to the net.
With BREADBOX64 you can post status messages and view your friends timeline. The timeline refreshes every two minutes. After starting you provide your twitter username and password separated by a colon. After pressing enter, the timeline is retrieved and shown. At the bottom of the screen there is an input field for you to type aq status message. Pressing enter will post that message to twitter.