I wrote my own Liveblogging platform, which turned out to be very simple to do indeed. Sadly, it’s not ready for release yet.
In practice, all you need is a page with a form which writes to a database. Now; liveblogs tend to get hammered, so I created a page which used my templates as a flat file (so no database calls).
Whenever I updated the liveblog with another entry, it wrote it to a flat file, and it showed the flat file to the user.
Rather simple, but brutally fast. Stood up to very high traffic on a small tech site you may have heard of.