Custom Games are new experiences that are created by the community, and playable within Dota 2. These games can be anything from a grand brawl between ten Invokers, to a story-driven dungeon adventure, to something creative that no one has seen before. For us, Custom Games represent a continuation of the tradition that gave birth to Dota, Team Fortress and Counter-Strike. We'd like to build an ecosystem where you can experience something new every time you launch Dota 2.

If you'd like to begin creating a Custom Game of your own, you can check out the second part of the update site[www.dota2.com] to learn more about the ecosystem we've created.

Later this week we will explore some underlying technology of the new engine.

credit to: http://steamproxy.net/games/dota2/announcements