Stacks is a simple and powerful kit to learn English tenses with 12 grammar bricks only.

3 levels to go - from 7 tasks in the easiest one up to 5 in the others.
4th level is to practice and test to make your grammar use self-acting.

It's even possible to solve each task just picking out the bricks and their sides.
If you face some troubles don't hesitate to press [Help] - you won't miss anything.