Lost of stuff you can do.
Best thing would be to buy a jump rope and start killing it! Take the shoes off and it will be alot less ruckus for anyone below you.
Also, you could get a punching bag.
You can pick a high point in your house (ceiling or edge of a wall or hang something) and do vertical jumps in sequence, touching the spot each time. Do 4 sets of 20 with 10 seconds rest in between, it will work you.
Get some boards and stack them, and alternate stepping up onto the boards side to side in rapid succession.
I also find that low weight, high repetition walking lunges and side lunges get me sweating like crazy. You don't need much room, just pace like a caged animal.
I just try to remember to keep your body moving, and make it hurt. You don't need to spend much loot or go outside at all. Just sweat it out.
