Epic Games has just announced it will allow its users to create games for the Epic Games Store. Valve currently allows users to create their own games, too, but Epic's self-publishing requirements are a bit different.
Largely, Epic allows users to make what they want, though there are two exceptions. The first rule is no pornographic content is allowed in a game, and secondly if you're making a multiplayer title, it must be playable across other PC stores.
Valve, on the other hand does not need multiplayer games to be playable on other PC platforms, and the free Steam multiplayer API Steamworks only works on Valve's digital storefront.
Epic CEO Tim Sweeney has heavily criticised this decision, saying to PC Gamer "Steam has created a real problem for the industry" with Steamworks.
"They have a classic lock-in strategy where they build these services that only work with their store, and they use the fact that they have the majority market share in order to encourage everybody to ship games that have a broken experience in other stores," he explained. "We were bitten by this early on with a number of multiplayer games coming to the Epic Games Store. Steamworks didn't work on our store, so they had either a reduced set of multiplayer features or none, or they were just limited to a much smaller audience back in the launch days of the Epic Games Store, so you had a lot of multiplayer games that really felt like they were broken."
Despite these criticisms, Steam remains incredibly popular, but with Epic now offering self-publishing tools, perhaps there will be somewhat of a migration.