The only download that I've been able to find of a 0.5.X version is on Github, where the download went smoothly, but the setup wizard refuses to work due to the more updated 0.6.2 already existing on my computer. The dilemma is that I want to hold on to both versions, believe it or not. Should I just get rid of 0.6.2, and install 0.5.1 as my only? Any help is appreciated, thanks.

Sorry for the late reply. The wizard doesn't let you have both an 0.5.x and an 0.6.x version as it simply tries to update the current version that is on your computer.

The most common way for runners to play both versions is to uninstall the game and re-install in the other version everytime you want to switch.

What I use is an application called "PortableApps" that lets you download portable versions of many apps (browsers, games, etc.). That's how I have both 0.5.1 and 0.6.2: 0.5.1 directly in my PC apps and 0.6.2 through PortableApps. I can't access other versions than the latest through PortableApps though, so I still uninstall 0.5.1 when I want to run 0.6.0.

I'm a little late on this post now, but you can try out my new SuperTux Launcher project, if you play on Windows. It aims to provide an easy way to play many SuperTux versions on one PC and possibly help you out.

https://github.com/Vankata453/supertux-launcher/releases

It's still experimental, so use it at your own risk, but try it out if you want - I hope it helps your case and others' as well. :)