Actual SLIP needed privs on the host to configure everything. slirp did it in usermode, allowing lowly undergrads to get real IP connections at home from the terminal services universities provided. Then you could run NSCA Mosaic at home :-) And ftp things directly, instead of downloading to your shell account tmp dir and using zmodem to transfer it the last hop.
https://www.linuxjournal.com/article/1174
It went away as real ISPs began to appear, offering PPP connections, and universities dropped their dial-in services. Strange and glorious to see it back again.
https://en.wikipedia.org/wiki/QEMU → "QEMU (short for Quick EMUlator)[2] is a free and open-source emulator that performs hardware virtualization."
However, the citation points to an article from The Register circa 2019: https://www.theregister.com/2019/03/11/windows_10_on_kvm/
So who knows?
Good grief, that's off by almost 15 years. Slirp was originally a SLIP endpoint you could run on a remote dial-in shell account to connect your local system to the internet. As it happens that's basically the same problem needed to get (something like) IP to work out of a userspace context in general, so it got appropriated by the container community and used pervasively. But it's roots go much deeper.
Also... "Quick Emulator"?!