Tekken Tag Tournament was released as an arcade game in 1999 before becoming a launch title for the PlayStation 2 in 2000. The arcade version operated similarly, but ran on a 32-bit graphics engine like Tekken 3. It received upgraded graphics when it was ported to the PlayStation 2. Its sequel Tekken Tag Tournament 2 was released in 2011.

Tekken Tag Tournament was notable for having the largest character roster in the series up to that point, boasting a total of 39 playable characters. 37 characters return from previous installments in the series, and two new characters, Tetsujin, a costume swap of Mokujin, and Unknown, the boss character in this game, were introduced. The most prominent feature is its tag system. A player selects two characters and may tag out between them to utilize special combos and throws. When in Team Battle mode, the fights are also tag fights unless there is one person left on a team where they will fight alone.
Source: http://tekken.wikia.com/wiki/Tekken_Tag_Tournament