Noctis.

Now this is an interesting specimen of gaming, an entire galaxy packed into a 1MB file. The game is entirely comprised of exploring the stars and the planets that orbit them. There are about 70 billion stars for you to explore in the entire galaxy. The planets you may find around these stars can often be landed on...unless they are gas giants or dangerous lava-worlds. The game is entirely free to download at https://anywherebb.com/ If you do decide to play Noctis, I really hope you don't obsess over amazing graphics...the current version of Noctis runs in DOS :P

DOS programs are known to be unstable in Windows XP and possibly even worse in Vista, but it's worth a try.