Players of the original Borderlands may remember that the game used GameSpy, a now defunct online gaming service, to connect players to each other. Being that GameSpy is no longer a thing, this means that players who are still playing the original Borderlands , couldn’t actually play with other players which made the game a lot less fun. Luckily this is going to be changed soon, as all the game’s online play will be navigated over to Steamworks.
Unfortunately, this means that gamers who purchased Borderlands on a platform other than Steam will now need Steam to play it. Steam is willing to dish out Steam copies of the game… buuuuuut it’s a bit convoluted. You’ll have to involved the “ Borderlands Granting Tool” on Steam. Then you’ll have to insert the original game disc that you installed Borderlands from. Then, you’ll also need your original activation key in order to get any DLC. It’s a bit of a mess, but its worth it for not having to buy the game again.
Many 2K games are also making this transition to Steamworks. Most notably Civilization IV made the transition only a small while ago.
Source: Gamespot