My eight year old son has a hard time distinguishing between a and ä when reading Swedish.
This simple app randomizes font, capitalization and word from a list of words where the first vowel can be either a or ä and use the Speech Synthesis API to enable the user to listen to both alternatives and pick the one it think is correct.
https://daghall.github.io/mvh/
The name is the phrase "Med vänlig hälsning" – "with kind regards" – without umlauts, making it "with regular chucking".