WebTerm is a Terminal emulator that runs in the browser. It uses v86 to create a virtual linux via WebAssembly and xterm.js as the terminal.
You can try out a hosted of WebTerm at https://webterm.onrender.com/ or clone the repo and serve the files with any webserver.
It takes about 20 seconds to a few minutes to download the ~45mb iso image and boot the system.
You can copy and paste text with Ctrl+Alt+C and Ctrl+Alt+V because Ctrl+Shift+C is already used by the the debugger.
WebTerm uses the v86 library to boot up a minimal Linux iso via WebAssembly and then attaches an instance of xterm.js to the serial port (/dev/ttyS0).
The Linux system is built via Buildroot. If you want to customize the OS, look at docs/buildroot.md