This simple-to-use app lets you take complete images and convert them into separate blocks or tiles. Simply load up an image file and specify the tile size (32×32 is the default). Hit the Process button and you’ll have hundreds of files ready for your use.
This is especially useful for SpriteKit programming, where Apple recommends splitting the image in the “Adventure” tutorial. Funny that they don’t recommend any tools to actually split the image like they did. Unfortunately it’s only for Windows at this time, but if there’s enough demand it will be ported to Mac.