Yesterday marked Steam’s first day of its new Early Access program, which gives select titles a chance to receive additional funding during development. Games in their alpha or beta phases can be found among the Early Access listings, including Arma 3, Prison Architect, and Kerbal Space Program.
Steam makes it very clear that the titles being offered aren’t necessarily finished, but purchasing them while in the development phase will give access through the alpha and beta phases as well as release. Some titles have multiple purchase options with benefits, while others are a single price with no tiers.
Do keep in mind that the products found in the Early Access program are going to have bugs and they are going to crash. Having played Gnomoria, which is on the list of games being funded, I can tell you that some of the issues can be a huge hindrance to actually playing the titles you pick up mid-development. Reporting bugs and aiding in the improvement of these games is part of the fun, even if it makes you want to punch something.
