Is that a Computer in Your Browser?
Two online emulator initiatives I found out about at the Library of Congress recently, at the Preserving.exe Summit:
The Olive Executable Archive, which originated at CMU and which is not open to the public yet, provides Linux VMs running emulators via one’s browser. When I saw it demonstrated, I was told it worked only on Linux, but that the team planned to have it working on other platforms soon.
JavaScript MESS, a port of the famous multi-emulator to allow it to run in a browser window. It’s not complete, but some of it is working and the code’s on GitHub. This one is an initiative of Jason Scott’s, with a great deal of work contributed by others.