We've heard of creative players embarking on some rather advanced projects in Minecraft, but this takes the cake. Modder SethBling has made a working BASIC interpreter within the block-ridden world. And "basic" is certainly the right word to use to describe how functional it is.
The magic behind the interpreter comes from an extremely large number of hand-written command blocks. Using an on-screen keyboard, you type in the program, which appears as banners on a massive whiteboard and then when you're done, you hit "Run Script" via a custom menu.
From the video, it can only print console output, but that doesn't make it any less neat!
It's also not the fastest interpreter ever written or the most flexible, but hey, it works. If you'd like to try it yourself, it's available as a download from SethBling's site.
BASIC Programming Language in Minecraft [YouTube]