I forgot to mention one more model which is kind of specific to games: open the engine/code, sell the assets (levels, etc.) which remain proprietary. This is an

I forgot to mention one more model which is kind of specific to games: open the engine/code, sell the assets (levels, etc.) which remain proprietary. This is an interesting compromise which seems to only be really available for games. Probably the most famous example of this approach is John Carmack's engines. (Of course, some games also get to enjoy this approach "against their will", namely when people like the game so much that someone reimplements the engine from scratch (see ScummVM)). Keeping assets proprietary doesn't really feel like a problem, since how do you open source art in the first place? Much art isn't really meaningfully modifiable after it's done, unlike source code. A .psd might have layers when a .png doesn't, but the difference isn't enormous. Art doesn't really have "bugs".