There's a free windows only game called Orbiter under continuous (ish) development since early 2000s. Its informative about the weird truths of orbital dynamics. Several years ago I went thru a phase of flying between Jupiters moons for fun.
There's probably a startup idea in creating what amounts to a E6B for orbital mechanics. The problem is making it elegant and easy to use. Anybody can open matlab/octave/mathematica/whatever and say "just enter a bunch of equations". I'm not sure the MFDs in orbiter are the wave of the future either. And its easy to get sucked into the trap of making it too simple for the .edu market such that it can't actually simulate anything. Its a hard problem. Maybe more for a PHD project because I'm mystified how to monetize.
If you're really bored you can run calculations on deceleration vs mass per surface area. From memory there are (admittedly extremely low) orbits where a rail-car shippable steel construction I-beam, actively pointed end-on, will orbit for months but a hot air balloon would deorbit in less than one full orbit.