Unknown Entity updated to 1.4.0 June 4th, and 1.5.0 today the 10th. 1.4.0 was the start to utilizing the gun, _GameMGR, and entities. 1.5.0 was mainly just a fixing and minor change version, and thus is not a fully announced update.
Both versions were released under Windows and Linux, and can be downloaded here.
Beta 1.0.0, the very next version, is mainly an optimization version, which may also feature the current entity firing at the player, and/or additional entity models. It will also have more settings in the settings menu (the current function of the Tab button will have all its graphical scripts moved to the settings menu, and Tab will then used simply to display FPS)
After that, Beta 1.1.0 is planned to feature gun zooming, a controls menu, at least one entity with shooting AI (if it is not featured in Beta 1.0.0), and possibly new levels
Beta 1.2.0 is a far future version that currently is only planned to feature power-ups and possibly more levels. Other planned features have no targeted release and may be released under any of these or none.