Old-school bodyweight exercises are very indoor-friendly, as well. If done with very little rest between sets, cardio and strength are both easily addressed:
-push-ups (modify on knees if need be)
-squats/lunges (sooo many ways to squat/lunge!)
-kickboxing (combinations of kicks/punches)
Press ups – incline, decline, normal. (If enough room try the bottom 1or2 steps of your stairs for incline/decline)
Crunches, half sits, full sits, V sits, Alt V sits, bicycles.
Plank, pulse plank.
Squats, air squats.
Tricep dips (Bottom of stairs or a chair)
A friend of mine does handstand press ups against a wall! Need to be careful of surroundings!
If I want to add some weight to my exercises I fill a backpack with odd bits from around the house, waterbottles, tins of food etc 1ltr water is 1kg, you can guage how much you are lifting then.
A military press is good, weight pushed out to the front back to chest and then above head and back to chest is one rep.
Planks and core workouts are also great.