I just came across this app on the MAS, there is also an iPad version.
It’s a pretty good app for diagramming just about anything you can imagine. The last couple of days I’ve given it a good thrashing and designed a use case, database schema, even mocked up a screen, for the price and what this can do, it’s a great inexpensive, easy to use tool.
https://itunes.apple.com/us/app/xdiagram/id517581636?ls=1&mt=12
Another one of their apps worth mentioning is ShortCut, this toolbar app allows you to create a menu of apps, giving you quick easy access to apps and folders you use on a regular basis.