First, do not confuse with Moosaic, the first web browser. Second, MOOsaico is a MOO (Object Oriented MUD, kind of) created 10 years ago in a Portuguese University (Minho's University, Braga) based on LambdaMOO code, heavily hacked for multi-language support.
MOO is old, had some lows and highs, but continues being my favourite talk-like system. Do not require any complicated software and is highly costumisable.
If you are that kind too, give it a visit at moo.di.uminho.pt:7777. You will find me there easily!