Chaos Island

Chaos Island is a lost hack, presumably of Sonic the Hedgehog 2 given that the screenshot in question shows an edited variation of Casino Night Zone.

This screenshot and the thread, are the only proof of this hack having existed at some point.

There aren't any archived snapshots of the thread so we have no way of knowing anything for sure.

The URL suggests that this most likely was, in fact, called "Chaos Island".