We built Intervals for the physical-therapy routine of our founder’s teenage son, then kept going. It is a timed workout app for rehab and training: build a program, choose how many days and sessions you want, or start from a free sample program.

What it does

Timed sessions: a sequence of exercises and rests with audio cues
Programs that group sessions over several days
A daily target bar that fills as sessions are completed
A free marketplace of sample physical-therapy, strength and fitness programs