Most of the starting city - Cyseal - is available, as well as some dungeons around the city.
Unveiling a new video, Larian Studios has announced that Divinity: Original Sin is now in Alpha stage for all of its Kickstarter backers - the Alpha version includes 15-20% of the full game (10-15 hours of content). Anyone that backed Divinity: Original Sin need only register or sign in on the Larian Vault, enter the email they used to back the game, and they will find a Steam key waiting for them under the Kickstarter tab..
Initially, the Alpha will be single-player only but multiplayer will be added in the future. Sounds and music, animations, and all that other good stuff may be placeholders to be updated as the Alpha rolls along. Alpha builds will be updated on a regular basis through Steam and players in the Alpha can capture and stream footage with no NDA.