Windows Subsystem for Linux (WSL) which lets you basically run linux kernel along side the windows kernel which lets you do a lot of cool stuff like containers, linux apps, whole DEs, etc.
It was pretty cool for like 5 minutes until people realized that keeping windows around was kind of pointless and we should just be running pure linux lol.
It's still a good feature, but it just gives you a direct comparison of linux vs windows which tends to outshine windows.
The naming of WSL sort of makes sense because it's actually build upon a kernel feature, which hass been mostly unused for more than a decade, called subsystems. There's the 'subsystem for Win32', which is the primary one that all Windows applications use, and then there were also the 'subsystem for POSIX' as well as the 'subsystem for 'OS/X'. WSL was simply a reboot of that technology.
The funny part is that this turned out to be too complex so WSL 2 ditched all that and simply uses a VM running the actual kernel in the background, so the name isn't even accurate anymore.
"subsystem for posix" etc. might be accurate but they put a WORD before it that messes it up. Now it reads like Windows subsystem, For linux. Yeah there is a software which is windows subsystem for linux. Its called wine. (Maybe W in wine stands for windows subsystem for linux lol)
What was weird was one of my friends who is "baffled by my choice of Linux" let me know about this subsystem and said "hey, look! There's no reason to use Linux again!"
It was pointless to keep windows at all. Pure linux is much cooler and running it inside windows was pointless. Unlike wine which runs windows programs inside linux which is big deal