jbot is a simple twitter bot modelled in functionality after a certain IRC bot employed at $WORK (the public version of which you can find as a rather horrendous perl abomination in the 'irc' subdirectory of the sources; there's also a HipChat variation in its infancy here). @jbot used to be known as j_b_o_t before it could take over the previously used @jbot account name.
jbot will follow anybody who follows him. Any messages by any of the users he follows will be analyzed for certain regular expressions that may cause jbot to chime in to the conversation with snide remarks or helpful commentary.
In addition, jbot also searches for any messages mentioning his name and will execute any commands found in those messages. Commands need to be in the format "@jbot !<command>". See this page for a possibly outdated list of supported commands.
jbot is Beerware. You can get the code from this tarball or from github. Contributions welcome! (jbot's twitter logo was taken from Flickr and does not in any way signify endorsement by Yahoo!.)