Exercise. It does wonders for your energy levels and your mental well-being. Plus it will make you feel you having done 'something useful' by the end of the day. The hardest part is getting out and starting - once you are busy, it is fun.

Otherwise, reading. If you have enough energy, read literary classics or non-fiction, the type that challenges you and/or teaches you new things. If you don't have enough energy, read something lighter - I am reading Alice's Adventures in Wonderland currently, for example, which is fun and relaxing. Finishing a book is a nice feeling, plus the mental focus on the story and on yourself can give rise to some nice insights on yourself, people, and the world.

Yu-Gi-Oh is more than a card game. It's fun and the way card effects can be chained together is a lot like programming in the corewars/redcode sort of way.

Others prefer to play Magic:The Gathering but after playing both we always end up going back to ygo.

Artistic activities might be a good option. That could be anything like painting, model airplanes, needlepoint, graphic design, interior design, to drawing. It will use a different part of your mind, generate a new skill and hobby, help you focus on something else, and can be totally offline if you want it to be. Plus if you end up doing a lot of whatever it is, you can sometimes sell what you're making.

I chat with friends, online or in person. I watch great movies, documentaries and tv series from around the world.

I find sleeping is good when tired

I go over my Anki cards.this focus the mind... Is conductive to sleep and very productive.

What's in the cards?

This seems like an ad

There are three carefully crafted posts in new where commenters mention this market, it's clearly some ad attempt.