Lost Alpha is a new episode of the S.T.A.L.K.E.R. series made by dezowave group for free!
We are testing the SDK public release, which is currently 2gb packed. It contains several test levels, and 4 story levels so you can see how we made the tasks, you can experiment a lot. We also include the written part of our knowledge base, which will help newcomers, or even advanced modders to create more quality content for the S.T.A.L.K.E.R. series. Thankfully most of the documentation is already avaliable on the wiki sites, or included with old stalker builds, we just updated them, and added our own notes where it was necessary.
All the updated editors (ae, le, se, pe), and xr tools are available (xrai, xrlc, xdro) which will let you create a bit bigger and more detailed levels for the game. These tools were created for the base Lost Alpha engine, which is numbered 1.3. Updating the base SoC SDK was necessary for the new rendeing modes, and game engine changes, as well to be able to handle bigger and more detailed levels.
Changes log and more info here: Dezowave.com