For realtime multi-voice synthesis, I keep using a not very well advertised side-project that performs reasonably well and also doesn't have a huge codebase: http://pippin.gimp.org/lyd/
Interesting weaseling of SourceForge is to add a "downloader" which fetches either the actual unmodified installer/sources. The "downloader" installs adware while fetching the real installer for the software. In the case of GIMP the filename of the downloader was made to be the same as the filename expected of the installer for a given version. This dirty approach might be thwarting ways of protecting with cryptographic signatures, or even trademarks/copyleft.
The official win32 gimp installers were not made by sourceforge, but by the GIMP contributor now locked out of managing the relevant sourceforge account. The same win32 installers that used to be provided on sourceforge are now provided from gimp.org directly http://download.gimp.org/pub/gimp/v2.8/windows/ the problem is the nice binaries being replaced by sourceforge made installers that also install adware.
jonesforth is a nice literary programming tutorial for making a forth using x86 assembly; and then forth - the same approach would work for implementing it in js, C or other languages.