Great documentation, standard features, speed, good support, continuous updates, great reviews - are the main things to check through...

I have just across a handy tool for matching fonts, called TypeGenius. Pick a starting font from the dropdown list and they'll give you...

Very useful collection of UI design guidelines for popular mobile and tablet devices.

Another useful resource, this time for iOS devices only. A good starting point when designing Apple apps for iPhone or iPad.

A good collection of responsive tools to ease the designers' and developers' pain.

Aaron Legaspi and Amit Jakhu have created the IxD Checklist, a handy interaction design checklist that we can refer to during every step...