Alan is a tool for creating works of Interactive Fiction, a.k.a text adventures. It is easy to use. It's focus has always been on the authoring aspects.
Alan consists of a programming language and a set of tools to support working in that language to create games, such as a compiler, various flavours of runners/interpreters, a completely integrated development environment, a map generator and so on.
Alan is in the process of moving towards version 3, and has entered beta state. This means that no incompatible changes are planned before release. So unless severe bugs or problems are found during the beta phase, games produced with a beta version should work even after release. So Alan V3 is now ready for supported production work.
There is still some material here for Alan v2.x but it is becoming more and more obsolete and will be removed with time. Unless you are having problems with an already developed game you should look at Alan V3. There is a converter and a conversion guide available to help out with porting an existing game to V3.