Here’s a library providing a nice set of flat buttons with great animations between them called VBPopFlatButton submitted by Victor Baro.

In total the library includes 9 commonly used buttons: forward, back, menu, download, share, add, minus, close, and an up arrow. The buttons come in two different styles – with or without a rounded background.

You can customize the background color (when a rounded background is used), the line color, the thickness of each line button, and the size of the buttons.

Here’s an animation from the readme going through the 9 different button styles available:

You can find VBPopFlatButton on Github here.

A great set of animated buttons.