HolyMorse

You learn each character as a sound, at full speed, so you never count dits and dahs. You start with K and M. A new character unlocks once every one you have is at 80%+ and fast. Weak and long-unheard characters come up more often. Words use only characters you've unlocked, and prefer words that contain your weak ones. Callsigns open with your first digit. Rounds are short and stop early if your accuracy drops, so your brain doesn't get worn out. Outside a round, tap a character to hear it. Colors show your skill: red is weak, green is solid.