I can recommend one 'hobby' above all, especially for programmers and all people working intensely on projects: rock climbing!

It's a great hobby/sport: It is free (just get the initial equipment: shoes and a harness), you'll get to wonderful places in nature, it's exciting and challenging, you'll get better very quickly and notice it, you'll meet many nice people, it's a great combination for using both body and brain(!), and most of all: It forces you to stop thinking about projects! If you climb, your mind will be _instantly_ free of all everyday business.

Imo the easiest way to start is finding a beginner climbing group around your location; there are plenty - especially in the US and Europe.