It's nice to see the progress being made regarding Arcturus over the past years and it really doesn't matter if it will be a closed source, you're the one programming it and people should not complain about that.
Just like you said, if you want open-source, fix it or build your own.
You've...
https://devbest.com/threads/how-to-set-up-a-retro-in-2021-iis-nitro-html5-part-2.92533/
Scroll down until you find the tutorial about the Nitro Converter.
Well the HTML5 clients are definitely faster rather than the flash clients, not many people know exactly how to set it up, so here's a ready-to-download pack from DevBest only for the HTML5 Nitro Client with Arcturus 3.0.0 Emulator
It's 1.05 GB in size, in contains the CMS, Database, SWFS...
I have tried and it works, its fast and the emu is great.
HTML5 Version
It's 1.05 GB in size, in contains the CMS, Database, SWFS, Emulator and all Nitro documents
Download: https://mega.nz/file/R0lADKRD#ePIEexnEF8AYpqKjx9Ru-3QL-MIYgFyFD_rV_XWh2Fc
Screenshot: https://prnt.sc/25wklat
Most die because they simply don't advertise or know how to switch from Flash to HTML5
Retro's have had their best times but it's not quiet dying.
Many people across the world still play on various retros.
Hablush is still alive and doing well with a great owner taking daily care of the hotel.