A few notes for you and others:
1) There are a few that switch sides/legs and I would handle them differently. For the lunges and step-ups, I think alternating sides is good. For the side planks, I think it would be useful to give the other side a whole segment. Splitting it in half wouldn't be much of a workout.
2) This is awesome because for the most part, you can modulate the workout however you want. In fact, keeping a log of the number of pushups/situps/high knees/etc would be cool because people could see progress. This might be a nice extension for the site!
3) It may be good to balance things out as far as muscle groups go. Pushups are repeated multiple times, as are squat related exercises. It is important to balance these out with the muscles that oppose these exercises.
4) Even better (at least for me) would be to have a series for desk workers that open up your body. We spend so much time crouched forward that a series of exercises to counteract this would be awesome.
Thanks and I hope you keep building on this!