Twoday is the software running at (among others) http://twoday.net, a german-speaking weblog hosting platform hosted and developed by Knallgrau. The software is in large part based on Antville and powered by Helma, a lightning fast, highly scalable Java web application server. Knallgrau hopes to be able to establish an active user and developer community around the twoday-software, and invites everybody to participate in development and discussion at twoday.org.
Twoday itself is released under an ultra-liberal BSD-style license (as Antville and Helma), which basically states that you are free to do with the software whatever you want. But still, make sure that you read and understand the license agreement (as well as the license agreements of the contained third-party code).