AdCat.io, is a design tool that allows you to upload a single picture to get perfect-sized, up-to-date ad images for Facebook, Instagram, and Twitter. It is 100% free, no signup is required, and it takes seconds!

Invision helps you create more realistic-looking prototypes without adding any extra time to your normal prototyping process

Pttrns is the finest collection of design patterns, resources and inspiration.

UICloud collects the best user interface designs and provides a search engine for you to find the best UI elements that you need.