Twister is moving to Apache's Incubator. It's actually going to be merged with an existing incubated project named Agila. Agila will have two major components: Agila BPEL (Twister) and Agila BPM. The first is the Web Service orchestration solution based on the WS-BPEL specifications and the second is an end-user oriented workflow.
The goal is to build a stronger community and to nicely integrate the two tools to answer to more needs than each tool separately (usually people doing web service orchestration need end user workflow interactions and vice-versa). Current Twister users don't need to worry, only the packaging is going to change a bit but all current interfaces will remain supported.
If you're interested or if you have more questions, don't hesitate to subscribe to Agila's user mailing-list (agila-user-subscribe incubator.apache.org). If you want to help us developing Agila, subscribe to Agila's developers mailing-list (agila-dev-subscribe incubator.apache.org).