Make little pixel pictures at your own pace. Every tap snaps to a square, so a wobble never smudges the drawing, and straight lines take just two taps: one for the start and one for the end. Nothing you do is ever lost. Undo as much as you like, and every earlier version stays in the history strip below the picture.
Every step you take is kept here, including ones you undid. Tap any picture to go back to it. Drawing after an undo starts a new branch; the old branch stays.