About a week ago I've build a 100% Swift App (one of my first ones, except for Notification Center Widgets, etc.) which also resulted in two open source components (both Swift) which I released and added to my Showcase.
This App basically serves to let the user create plain colored wallpapers for his iPhone or iPad by moving his finger around.Up- / Downward movement changes hue whereas left- / right in the upper part changes saturation and in the lower one brightness.
Grab it on the App Store...
...or see it in action in the video.