They can always try to sue the creator, but that probably won't get them anywhere, especiallyi since there are offshoots of it and it's essentially gpl'd (MIT License is very similar). Also, as BT only dl's and ul's one file per instance, the damage model the RIAA has been using no longer applies. They only seem to be capable of suing people who are sharing massive libraries of mp3's. The plaintiff would essentially have to argue that every person who is sharing a given file is joint and severally liable for the damages for sharing with each other, thereby bringing the dollar figure up. Doesn't wash in my analysis. It could cost the RIAA thousands of dollars to collect $20.