*Update #2: Since I posted this article years ago, the digital distribution market on PC has grown and branched out a great deal. Impulse has been purchased by Gamestop and Direct2Drive has been purchased by Gamefly. However, some great Steam alternatives that I still use and highly recommend include:
There are many, many, more digital distributors, these are just a few that really stand out. Be sure to shop around before you buy! You can use a site like CheapShark to easily compare digital download prices, all in one spot.
Impulse allows you to purchase and instantly download games, much like Steam. One thing that sets Impulse apart however, is that it does not need to be running in order to play games you have purchased. This means instead of having to wait for the service to start every time you want to play, you can jump right into the game. The Impulse client itself starts faster than Steam, and has a very slick interface, as is the case with most Stardock products. There are tabs for products, community, updates, your software, and your games. Updates are readily visible when you start the client, and require a few clicks to execute.
So, like anything else Impulse has both its advantages and flaws. I would expect that as time goes on the service will only get better, and I wouldn’t be suprised to see it doing as well as Steam eventually. Only time will tell.
*Update: It looks like Stardock is working on a buddy/matchmaking system, it looks promising. Check it out here.