This website features a pretty bare synth coded with JavaScript and Web Audio API (the whole thing being run by Symfony). It is playable using the keys of your keyboard or by simply clicking on each key (touch works on mobile).
You can try it at shitty-synth.ghartemann.fr.
It isn't a good synth nor does it work without issues. The main ones being that click sound happening at the end of each tone or the inability to play multiple tones at once or to switch from one key to another efficiently.
Please keep in mind that it's been developed in less than three days and is very, very much a WIP.