One of the most important elements of software development is a good user interface or UI. While the adding, editing, processing, reporting and deleting of data is foundational, a good GUI can make the difference between a successful and a failed UX (user experience).
All good software starts with a good UI design. And in the world of mobile apps that is even more crucial than ever before. Ease of access, readability, functionality, colors, etc. all contribute to an app's appeal and usefulness.
One way to get started quickly in the app design process is by prototyping. Here are some UI prototyping tools you may find helpful:
1. Fluid - a web-based prototyping tool that's fast and easy. https://www.fluidui.com/
2. Concept.ly - a web-based tool which allows for collaboration and feedback. Currently free. http://www.concept.ly
3.Pidoco - rapid prototyping tool: https://pidoco.com/en/lp/paper-prototyping?piwik_campaign=en_P61_paper-prototyping&piwik_kwd=paper%20prototyping
4. Hot Gloo - free wireframe prototype tool: http://www.hotgloo.com/
5. Mockflow - super easy wireframing mock-ups: http://www.mockflow.com/
6. Keynotopia - PowerPoint-based templates & graphics for mobile UI development: http://keynotopia.com/