Found my HIIT tool of choice for home: Deadmill sprints!
For those who might not know what they are, instead of letting the treadmill motor make the belt move fast, you turn the treadmill off and instead push it with your own power. I like these as it activates your upper body too, has a quick transition (vs time lapse while belt speeds up) and is easier on the joints. Did I mention it is intense?! Go 15/20 seconds on the sprint, then I just do a lap walking in my basement for the recovery.