Windows Keyboard Fixes disables the sticky keys dialog while Minecraft is running and also makes the Windows key not show the Windows startscreen when having the keybindings GUI open or when there is no GUI open / when you control your character, so it can actually be used for gameplay input. If you already have the sticky keys hotkey setting disabled the mod will not change it.

FAQ

Q: How was this done?
Sticky keys: When at the title screen / when the game is finished loading the mod sets a system wide flag to disable the sticky keys hotkey setting through Windows' APIs. When closing the game the setting is then reset.

Windows key: I basically use a low-level Windows keyboard hook to let every other key automatically through other than the Windows keys. The Windows key is only let through normally when a GUI screen is open other than the keybindings screen.

Q: Why disable sticky keys system-wide?
Because even Microsoft's own documentation says to do so and as far as I know there is no other way to do it, even a few other games I tried that disable it all disable it system-wide.

Q: What happens to the sticky keys setting when the game crashes? What happens if I run multiple instances with the mod?
The mod writes information to the Windows registry (HKEY_CURRENT_USER\SOFTWARE\Minecraft\Sticky Keys) to remember what to reset the setting to when closing the game and what other processes with the mod are currently running. The first one to start get's to change the sticky keys setting and the last one to exit get's to reset it.
In the case of a crash there is also a dormant thread that get's executed to reset the setting on the shutdown of the Java VM. This is also executed when Java is killed from Task-Manager.
If the crash is however very severe (as in probably crashing the entire VM, but I don't think that happens often) or if a power outage occurs the setting will be reset the next time Minecraft is started & closed with the mod.

Q: Isn't 1/2 of the mod kind of pointless, when one can just change the sticky keys setting?
Yes. However some people, including me, automatically just hit "No" and always forget to change the setting afterwards.

Q: What happens to Windows shortcuts that use the Windows key?
Most are none functional when the key is not forwarded to the entire system. A few however, like Win+L to lock the desktop, seem to be so engraved into Windows that they are still let through.

Q: Can I use this in a modpack?
Yes