Comment by PrimalPower

Tai Chi is interested. It's essentially a standing form of yoga.

IMO, in theory it's even more useful for desk workers than yoga.

If you look at the history of Ashtanga Yoga, it was primarily developed for the traditional life. Where even non-laborers spent a significant amount of time on their feet and moving around. This is why doctors, nursers, actors, laborers, retail workers, etc... sing praises about yoga. I struggled to get much out of it, as I found it stretched the stuff that wasn't that tight for me and didn't focus on my problem areas.

The martial arts background of Tai Chi, alongside the pivot to longevity focused practices in East Asia, makes Tai Chi uniquely suited to the woes of a desk worker.

Unfortunately Tai Chi lacks serious standardization or centralization, so it's hard to know if a particular school/class will work for you nor is it as easy to self-study.

Of course, you don't need the Eastern traditions to obtain these same benefits. Dynamic stretching, Pilates, and functional strength training can work too, but I find that the eastern stuff has a meditative/spiritual aspect that regular training does not.