We've all heard of Twitter; some of us are even on Twitter. The new and interesting online "toys" I've come across recently are Woofer and Squeaker. Woofer is macroblogging: it requires a minimum of 1400 characters before it sends; Squeaker requires exactly 14 characters before it sends. Both of these are a lot harder than it sounds (try it!), but could be an interesting tool to use in the classroom with students.
The downsides to this are that it's on the internet, so it's not as controlled and private as might be preferred; the other is that the students are required to have a Twitter account to utilize these. Both might preclude elementary usage, but for secondary students, it can be a great way to work with them on precision in writing. Try them out and tell me what you think! :-)