Three20-P31 is a project mainly written in ..., it's free.
Used to be a Three20 fork, now it's categories and additions to Three20.
Additions to the Three20 library. To use, make sure "Three20/Three20.h" is in your projects .pch file then just drag the P31-Additions folder into your project along with the P31.bundle.
The P31-Additions project included is simply a static library the links in all the Three20 modules. It serves no real purpose and is just used to test compilation of the files as they are changed.