There are plenty of fancy elliptical machines on the market that can give you a good workout. Most of them don’t fit under your desk though. The MERACH E12 is a versatile elliptical machine with 3 modes, including a climbing and under desk mode. It has 16 levels of electromagnetic resistance and an app for workouts and tracking.
You can remove the handrails to use this elliptical under your desk. There is also a climbing mode to further push your body. This exercise machine has an app with workouts but also works with Kinomap. It has a footprint of 46.5×24.8×61.8 inches with max weight capacity of 330lbs.