Ed Felten has written a P2P application in fifteen lines of Python code – cool!
TinyP2P is a functional peer-to-peer file sharing application, written in fifteen lines of code, in the Python programming language. I wrote TinyP2P to illustrate the difficulty of regulating peer-to-peer applications. Peer-to-peer apps can be very simple, and any moderately skilled programmer can write one, so attempts to ban their creation would be fruitless.
Pointed out by Donna Wentworth on the indispensable Copyfight.