Status
PicoContainer 3.x is in Git at Github and Codehaus (mirrors), and is a work in progress.
PicoContainer 3.x is good enough to use in production, but it is not finished yet.
Goals over 2.x
The major piece that's taking a while to do is JSR 330 compatibility, and is more or less complete.
2.x
If you want the previous PicoContainer (2.x), it is still at Codehaus in Subversion:
Source here: https://svn.codehaus.org/picocontainer/java/2.x/trunk
Binaries here: https://nexus.codehaus.org/content/repositories/releases/org/picocontainer/picocontainer/
Web Site
The Website for PicoContainer itself is picocontainer.com
Presently, it is for the 2.x series of releases.