This is a list of things to do when releasing a new version.

Preparation

Update version number in CMakeLists.txt
Update version number in src/Tests/guitar-adnote.xmz
Update Copyright (mainly YEAR) info in src/UI/MasterUI.fl (note this is mentioned 2 times on line 5 and line 872)
Update AUTHORS.txt to included new contributors since the last release
Check and update (if needed) the manpage file : doc/zynaddsubfx.1.txt
Check NEWS.txt contains all the changes since the previous version

Build and test a release candidate

Check the code builds on Linux: no gui, fltk, ntk, zest. Standalone and plugin versions.
Check the code builds on Windows: zest. Standalone and plugin versions.
Check the code builds on Mac: fltk, standalone only.
Check the docker containers produce binaries
Check the code runs on Linux, Mac and Windows (standalone and plugin versions)

Then tag the release git commit with the version number (zynaddsubfx, mruby-zest-build).

Publish the new version

Build tarballs
Upload source tarball to sourceforge website
Update the "Linux/BSD/Source" link on http://zynaddsubfx.sourceforge.net/download.html (do that here : https://github.com/zynaddsubfx/zyn-website/blob/master/download.html)
Update news on sourceforge website (https://zynaddsubfx.sourceforge.io/news.html)
Issue release announcement to linux-audio-announce, zynaddsubfx-user, kvr, linux-musicians