Well, I come to seek help from the good folks here. I am in the last 6 months of my PhD research and on the verge of a crackdown, so I need something really soothing. You know, something simple, slow paced, preferably running in a window and that can provide some experience like old solitaire did (the one in windows 8 is just plain horrible) for a 15 minute break with no strings attached. I've recently bought Critical Mass on Steam and it is the opposite of what I want. Any good suggestions?

Edit: if it can be played on keyboard only, so much the better.

Try Reus, it's a RTS that you can easily stop or take breaks from.

It was on the last Steam sale, wasn't it?

To the Moon

EDIT: Sorry, it needs mouse as well.  

I agree with Plants vs Zombies then.

Yes, it was part of the summer sale, I tried it and it's pretty neat, you can play it in short sessions since it's like a mini Civ.

One of the first things I got for my IPad three years ago and the best tablet game alongside the 2 infinity blades. But way too addictive for what I'm searching. :D Appreciate the try though. ;)

Solitare on the PC is the best game to go. In those 15 minutes you can do several matches. But maybe that's me, I love solitaire!

Proteus.

Just walk around, explore, listen to the sounds.
http://store.steampowered.com/app/219680/

http://www.cambriangames.com/Phyta.zip

Limbo was a short 4 hour game you play with just your keyboard. Very soothing too.