Just announced a couple of weeks ago, the Virtual OS Museum by Andrew Warkentin is now available. Featuring over 1700 emulated computer operating systems organized through a dedicated GUI launcher, this amazing project is sure to bring you hours of pleasure. The first 6 or 7 hours being downloading and unzipping this 175GB resource. The emulators are pre-configured and ready to start. You can also add in your own image files and see how they work in emulation.
There is also a personable Discord channel where you can troubleshoot with Andrew and communicate with the growing community of users.