This allows you to transperantly proxy ftp and redirect requests via a squid cache... neat. This gives you a way to transperantly proxy and cache ftp from non-ftp-proxy aware ftp clients.
At first glance it appears to be fairly minimal and clean. The only potential worry for larger sites is it's one thread/connection model might not scale well, particularly as ftp connections tend to be more long-lived than http.
An open, cross-platform journaling program.
A scientific plotting package.