Qataki is a shell script that you can use to read/post notices from the command line in a simple manner. It supports Identi.ca, Twitter, and StatusNet. You can post, reply, retweet, or send direct messages; read personal, public, and user and group timelines (last statuses); read messages directed to you (i.e. where you are mentioned); read messages in context (conversations available only for Identi.ca/StatusNet); and search for notices.
Chyrp is a blogging engine designed to be very lightweight while retaining functionality. It has powerful theme and extension engines, so you can personalize it however you want. The code is well-documented, and it has a very strong structure that's loosely based on the MVC design pattern. Chyrp allows importation from several different blogging engines and uses a system called "feathers", which are basically templates for custom posts.
Xpostulate is a blog/microblogging client that posts to Livejournal, InsaneJournal, IziBlog.net, DeadJournal, Scribbld, Inksome, Wordpress, and DreamWidth. It can tweet to twitter.com and dent to identi.ca so that you can announce new articles. This is all done via one interface, saving your login information for each, and thus simplifying cross-posting to your various social networking sites.