Realistically there isn't really any commercial value left in it though. While there were some notable unique games made with it (Titanfall 1 & 2, E.Y.E, The Stanley Parable, etc), these were made over a decade ago and the majority of games made with it are reworks/mods/adaptations of Half-Life related material.

https://developer.valvesoftware.com/wiki/List_of_third-party...