Funny site before the weekend about fake update screens: fakeupdate

Prank your friends and colleagues with fake update screens!
Press F11 to go fullscreen
Press ENTER to cause a BSOD

You have the choice between the following operating systems:

• Windows 98
• Windows XP
• Windwos Vista
• Windows 7
• Windows 8
• Windows 10 Install / Update
• MacOS
• SteamOS
• Ubuntu

And the demo

Another funny websites:
Windows 93
PCjs Machines : home of PCx86, the original IBM PC simulation that runs in your web browser. It is one of several JavaScript Machines in the PCjs Project, an open-source project
V86 (demo / github) : v86 emulates an x86-compatible CPU and hardware
The Restart Page : a tribute to the most significant operating systems that has been part of our geek lives