I love experimenting: exploring the unknown (or proving the known), often just for personal knowledge. I guess that’s the reason why every wannabe game programmer tried at least once in his/her life to write a game engine from scratch. That’s not exactly the case of Peter Rakos, an expert, who wrote a 3d engine just using Microsoft Excel (and his brain).
Intriguing, isn’t it?
I seriously recommend you to give his article a read, trust me. You can find it here, at Gamasutra.