Ataxx is the real original game by the authors mentioned at the Assimilation rules. Due to a former misinterpretation of the rules, this one was added after Assimilation. There is only one (but important) additional rule:
A piece can be moved 2 spaces in a L-shaped jump, identical to a knight move at Chess. This move causes no duplication, the piece is really moved and disappears from its former position.
All other rules are the same as for Assimilation. Play this game