Knytt Stories is a wonderful free platformer. Extended Version is my mod for it.
In order to play Knytt Stories Ex or any other version of Knytt Stories with proper FPS you need to either adjust your monitor refresh rate or use a compatibility setting. Refresh rate of 75 herz works pretty well, 100+ would be ideal. As for the compatibility setting, to access it in Windows 7 or Vista open "Knytt Stories Ex.exe" properties, go to Compatibility tab and check "Disable desktop composition". Windows 8 and 10 don't have that option. There are programs that can temporarily disable desktop composition (WDM) in Windows 8, but it's said that they don't work in newer versions of Windows 10. WDM aka Aero is the thing that allows effects such as transparency in Windows starting with Vista, but causes a very crude forced V-Sync for all windowed mode applications, degrading FPS and making it unstable.

Extended Version v1.5.9

• Mod Download
  Extract into your KS folder. Don't worry, it's compatible with all other mods and won't hurt anything.
• All in one
  If you don't have Knytt Stories installed, use this archive. It includes all needed Knytt Stories files.
  
• Discussion
  Here you can discuss it and find some information.
• Source Code
  If you want, I can provide you with all needed MMF2 extensions.
• Example Level
  A small example of stuff KS Ex can do.
  
• Ball Tutorial
  A tutorial level introducing the ball mode. Version 2 contains two new secret endings for skilled players. Discuss it here.
• Platforms Room
  A single room level with falling platforms. Discuss it here.
• CO to Template
  A tool to convert custom objects to template objects.
• Template Objects
  A thread about using and making template objects, with downloads.
• Graphics of Standard Objects
  Graphics of some standard objects ready for replacement.

Scaler for MMF Games v1.0

Can be applied to any game made with ClickTeam Multimedia Fusion 2 or its predecessors that doesn't use DirectX for graphics output. Makes the game scale to whole screen without the need for resolution change. Also lets you remap keys. Very useful for Knytt Stories Level Editor and older Nifflas' games, especially Riddle and such. Level Editor was the reason I've implemented Windowed mode option.

Trivia: Multimedia Fusion 2 is the visual game creation program Nifflas used in the past. In case you wonder if it's any good, it isn't. It's hard to overstate how bad it is. It's very impressive what Nifflas managed to achieve with such a bad tool.