Dahdidahdit app
Copying Morse code has to be done in the head. Using computer programs that allow for easy keyboard input of letters makes it easy for learners to wire Morse code symbols ("dahdidah") to positions on the keyboard, making it next to impossible to copy Morse code when no keyboard is available: You know ditditdahdahditdit is at the upper right corner but when you finally remember that's where the "?" is, DX has already sent 5 more letters.
Dahdidahdit just plays Morse code symbols. Learners copy the symbols by handwriting to a sheet of paper and later compare with what was sent. The learner then counts how many errors were made. Dahdidahdity keeps track about this and, when the learner makes progress, teaches a new letter or increases the speed.