This is the free version of the Random Timer. The premium version also has Save/Load functionality and is called: "Random Timer (Reaction Drills)".

The random timer is especially useful for martial arts and other sports that require explosivity or quick reflexes.
Here are some example exercises for various sports:

Example exercise for cardio:
Perform jumping jacks for 3 minutes. When you hear "Down", go down and do a pushup, when you hear "Up", jump up and raise both your knees.

Example exercise for boxing:
Perform a boxing run (cardio exercise) on a heavy bag. When you hear "1,2", quickly give a jab and a cross. When you hear "3,4", give 2 powerful hooks. Set the timer to end after 3 minutes.

Example exercise for karate:
Do a reverse punch when you hear "Quick", a mawashi geri when you hear "Strong", and a counterattack when you hear "Defend". Set the timer to 2-5 seconds, and stop after 30 repetitions.

Example exercise for football:
Sprint on an agility ladder, then break left or right when you hear "Left" or "Right". Repeat 10 times.

Example exercise for Brazilian jiu jitsu:
Perform stationary Ebi (hip escapes), then practice a sweep if you hear "1", or a triangle if you hear "2". Repeat 100 times.

Example exercise for MMA:
Shadow box, then sprawl if you hear "Down", and perform a powerful combination of attacks if you hear "Attack". Repeat for 5 minutes (a full round).

Example exercise for basketball:
Dribble around freely, then pass if you hear "Pass", shoot if you hear "Shoot", or accelerate with a crossover if you hear "Go". Keep going for 3 minutes.

Example exercise for Taido:
Move around in unsoku, and when you hear "1", "2", "3", "4", or "5", perform a Taido Sotai attack using "Sen", "Un", "Hen", "Nen" or "Ten".

Explosive training:
Dribble on the spot. When you hear "Left" or "Right", quickly step to the side, squat & touch the ground, then return and continue dribbling. You can also add the "Up", "Down", "Front" or "Back" commands to the random timer to make things more difficult.

The random timer can be used for more things than just reaction drills or explosive training. For instance, you could also use them for games, ie hot potato.