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If you're mainly interested in changing the hidden features, I can also recommend Deeper (by the same developers).
 
im running Onyx 1.8.5 for Leopard. i dont use it that much though as you dont need to run maintenance tasks every day. also look on versiontracker or macupdate if you cant work out how to download it from the devs. if you want the hidden features ill will also suggest Deeper
 
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