Tobyfox is launching Undertale on Xbox, so you can purchase it or download it via Xbox Game Pass on Console. From what the presser states, it won’t be available on PC and is strictly on console.
Undertale has been around for some time on PC, (which recently celebrated it’s fifth birthday) by streaming a free concert on YouTube, but you should check that out after finishing the game.
What makes Undertale a unique experience is how the game approaches things. For one, every monster you encounter in the game is a unique experience, some you can fight, others you can be merciful to, and these decisions culminate and affect the outcome of the story. It is the case of characters players have fallen in love with over the last few years and it’s exactly why the game is still held in high regard today.
I’d highly recommend checking the game out when it launches tomorrow.