Black Mesa mod ties Portal to the original Half-Life.

Crowbar Error 42 writes "Its been very heavily hinted at that Portal is set within the Half-Life universe but like many things added to the Half-Life universe in the sequel and in the following episodes there is no mention of things like Aperture Science in the original game.

While there is nothing Valve can do about it as hopefully they are hard at work on Half-Life: Episode 3, it looks like the creators of the Half-Life 2 mod, Black Mesa are hiding small references to Portal in their mod."