It isn’t a mod yet, TF2 is a full game and a sequel to the original Team Fortress. As to my knowledge it still hasn’t been open to beta’s, but this was about 3 hours ago and they may have opened up beta’s by now.
Orange Box is basically 5 games for $50 ($45 if you pre-order off of Steam). Half Life 2, Half Life 2: Episode 1, Half Life 2: Episode 2, Team Fortress 2, and Portals. I already have HL2 and Episode 1, but I can use the keys for HL2 and Episode 1 elsewhere, so 3 games I don’t have for $50 is not a bad deal 
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