There are some games that don't have official ports but do have open source rewrites like The Settlers 2. I have created a preliminary Gentoo ebuild for this and other games with official ports. Their packaging format (innosetup) was a total bitch to work with (we had to use Wine to extract) but someone very recently wrote a native Linux extractor. I haven't had chance to try it yet but it must have been quite a task. It's a very complicated format.