It is on sourceforge:
Skulls! Multi-Network WebCache download | SourceForge.net
In the latest version there is already the block of bad IPs on update; the change regarding distribution of blocklists to clients isn't yet complete.
The dependencies are really few:
1) PHP 4.3 and higher (the latest version would be better for security).
2) fsockopen or curl (this is used for alternative url checking, but it could work without it; in this case the url exchanging will be disabled but the other things will still works).