OpenEar is built on tone.js: https://github.com/ShacharHarshuv/open-ear

limut implements WebAudio and WebGL, and FoxDot-like patterns and samples: https://github.com/sdclibbery/limut

https://glicol.org/ runs in a browser and as a VST plugin

https://draw.audio/

"Using the Web Audio API to Make a Modem" (2017) https://news.ycombinator.com/item?id=15471723

gh topics/webaudio: https://github.com/topics/webaudio

awesome-webaudio: https://github.com/notthetup/awesome-webaudio

From the OpenEar readme re perfect pitch training; https://github.com/ShacharHarshuv/open-ear :

> Currently includes the following built in exercises:

> [...]

> 7. Interval recognition - the very popular exercise almost all app has. Although I do not recommend using it as I find it inaffective in confusing, since the intervals are out-of-context.

Interval training is different than absolute pitch training. OpenEar seems to have no absolute pitch training.