I have recently added IP blocking to Skulls GWC in addition to a lot of other changes.
It also include a predefined list of spammer IPs, this should improve the P2P connection phase by reducing the amount of spam hosts to the minimum possible.

There is anyone interested to host it and report bugs?

PS: This change is NOW in the last release (0.3.2).

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Skulls! Multi-Network WebCache

You have it hosted on github or somewhere? I'd try it. Can't promise I'd leave it up forever. What are the dependencies? Anything special it needs to run?

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).

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Skulls! Multi-Network WebCache

6 hosts listed, as of today. I have no application using myself yet.

All looks good so far.