Steam, an online distribution platform for videogame content, has signed up more than 13 million users, the system's owners Valve has said.
More than 150 games can be downloaded via Steam
More than 150 PC games can be downloaded via Steam and the system has also been used to automate more than 2,500 updates to existing games.
Digital distribution of game content is a growing segment of the industry.
Sony, Microsoft and Nintendo have all started online services for downloading games onto consoles.
Gabe Newell, president and co-founder of Valve, said: "In Steam's case, we have millions of customers who are gamers and dozens of customers who are developers and publishers.
"In the past year, we've added over 100 new titles from third parties, grown to over 13 million active accounts."
Steam was developed as a way to auto-update Valve's multiplayer games but now has evolved into a platform used by many leading publishers and developers.
Xbox Live is one of the successes for Micosoft
Games such as Call of Duty 2, Top Spin 2 and Half Life 2 can be downloaded via the service.
Microsoft lets Xbox 360 users buy and download arcade-style titles via its online service Xbox Live.
New and classic titles can be bought for between £3 and £10, and the service also offers downloads of game demos, which have become an increasingly important way to market a net title.
Thousands of people downloaded the beta version of Halo 3 recently, the first time a trial version of a game had been made available online to Xbox users.
Sony and Nintendo offer downloads of classic gaming titles via their PSN and Virtual Console services.
Stephen McGill, head of gaming and entertainment marketing at Microsoft UK, said Xbox Live Arcade had put games into the hands of players that they would not have been able to find in retail.
"These are classic titles that are no longer sold in the High Street."
But he said the current limitations on broadband speeds and the increasingly large file sizes of blockbuster titles meant digital distribution had a long way to go yet.
"If that future is out there, it is out there a long way away. Until broadband pipes get fat enough, there will always be a place for the High Street and online retailer."