I have a desktop app that I access remotely. Not browser based and not designed as multi user. I use Real VNC hosting on the notebook/server and then use the VNC viewer app on my Android phone and other notebooks to access it. That might be an option. Relatively easy to set up. But would require the VNC viewer app for anybody wanting to access it.
Occam’s razor. Probably something out there, as this is not a unique requirement. Have you asked other retirement communities what they use to schedule shop time? Or a local maker space?