Wine
Wine is a compatibility layer providing the possibility to run many Windows apps/games on Linux.
Boxedwine
Boxedwine is an emulator that allows Windows applications to run. It accomplishes this by using an unmodified 32-bit version of Wine, while emulating the Linux kernel and CPU. It is written in C++ with SDL and is supported on multiple platforms.
Boxedwine runs in browser too. Speedy Eggbert runs in Boxedwine in browser, but is too slow and buggy.
External links
https://werat.dev/blog/how-wine-works-101/