With the JUCE framework being mildly open-source, I’ve been an avid and long time contributor and user - over a decade at this point!
Many bug fixes and typographic errors aside (which I really just prefer helping out to sympathise with maintaining such a massive library), I’ve contributed an assortment of features. Note that I’m excluding from the VST3 client and hosting because I cover this in a separate page.
In no specific order, here’s what I’ve contributed:
Added the VS2012 to VS2017 exporters to the Projucer
UUID functions and documentation that is to RFC spec
FMA3 and FMA4 detection support
Pushing for ValueTree::appendChild
More constexpr!
Added tons of metadata support to the WavAudioFormat
Pushing for the XML and Lua tokenisers
Lots of Windows audio driver (WASAPI and ASIO) fixes, especially regarding sample rate changes
Lots of UTF conversion stuff