I have been aware of folks using gadgets like the MagneTrainer while sitting in their normal office chair.
A fancier version of this idea can be found in the FitDesk:
You can also ride a full-fledged bicycle while you work, like this one from Kickstand Furniture:
And, of course, there are DIY folks making their own bike desks. This design straps a simple Brada laptop support to the handlebars of a stationary bike:
Much more to come on this topic, for sure.