Here is my Tumblr ask and the response Undertale gave:

I asked: My computer is p shitty but I'm definitely interested in this game; I love your work. (The making of the Earthbound Halloween hack was an interesting read; I still need to play it!) Do you have an estimate for the lower-end of the computer spectrum able to run this game? If a Linux release is made in the future, would I have to buy the game again? And lastly, being DRM free, I do not need Steam to play it? Sorry for these excessive questions, I hope I'm not asking you something answered earlier!

Undertale answered: Yes you can buy it DRM free on the undertale website. People were able to run it on a windows XP with like… 3 gigs of RAM or something? It’ll probably be playable