Open source editor [on hold]

I want a simple, highlighted source code editor for iOS, Mac and PC. What's my best bet? Can you recommend some portable open source editor?

Or is it easier to just build it from scratch on all three platforms? I read somewhere that iOS 7+ comes with built-in support for different colors in the editor? What about wx? Qt? Some other framework?

I'd love to hear from someone who did this already!