Internet Archive lets you play one of the earliest computer games Space War! emulated in JavaScript in the browser.
This entry covers the historical context of Space War!, and instructions for working with our in-browser emulator. The system doesn’t require installed plugins (although a more powerful machine and recent browser version is suggested).
The JSMESS emulator (a conversion of the larger MESS project) also contains a real-time portrayal of the lights and switches of a Digital PDP-1, as well as links to documentation and manuals for this $800,000 (2014 dollars) minicomputer.