Lost Alpha is a new episode of the S.T.A.L.K.E.R. series made by dezowave group for free!
It's nearly completed, we worked a lot on this feature, when we disabled it back in 2013 it looked totally different, now it looks more modern, and easy to use.
In short, you will gather points during your stay in the Zone, which you can spend on various skills. Each has pros and cons, but you won't be able to max all of them, so you will need to choose wisely!