Bohemia Interactive has released a new update for the Arma 3 Alpha. Aside a wide number of tweaks and optimizations, version 0.54 of the Arma 3 Alpha implements a new fog technology, adjustable sidearm stances and further stability fixes.
Arma 3 is still available to buy on Steam which will give you access to the full game. Or if you don’t want to pay money you can get yourself an Alpha lite code from anyone who has bough the full Alpha build. How ever Alpha lite does not support online mode.