I have found a very useful BIOS simulator for Lenovo machines. This has a very long list of Lenovo machines and you may open each BIOS to see the options and how it works. These seem to be very popular, you may see where all the options are and fiddle with them without breaking anything.
Find it here: https://download.lenovo.com/bsco/index.html. Good for training I guess, or to just play around with.
Here is something else I found, some online Cisco routing and switching simulators. These would be invaluable for practising some Cisco networking tasks online, visit the site here: https://asecuritysite.com/Cisco/general?Length=5. A very good site with a few tasks to complete using the online emulated routers and switches. There is an online Cisco Packet Tracer instance here: http://pt-anywhere.kmi.open.ac.uk/. Very useful to use to learn Cisco networking on any computer.
Speaking of emulators, here is an Apple II emulator coded in Javascript. This can load various disk images and run some productivity software all in an emulated environment. This is amazing.
Visit the site here: https://www.scullinsteel.com/apple2/