Guillaume Bort's Play Framework based on Java and Scala, a programming language, which runs on Java Virtual Machine. Its lightweight architecture gives you the possibilty to develop user friendly web applications with minimal resource consumption. A advantage of Play is the non-use of Java EE constraints, so the realization is compared to other Java-centric platforms much easier. Furthermore, you can combine a lot of available modules and plugins with Play. Most of them are available on documentation page or GitHub. Try it and love it.

InK Interface Kit is a free flexible web framework by SAPO, Portugal, which allows you to create extended web solutions by multiple shortcodes. InK comes with a fine icon set, based on Font Awesome, with over 200 pictograms. Multiple beautiful forms, alerts or tables are available for your choice. A fine feature is the Ink JS UI, which will be delivered with all what you need to build userfriendly web applications, overall helpful js components, like progress bars, image queries or tabs. 

UIkit by Yootheme is a stand alone web framework, which allows you to build lightweight and well-structured websites by the help of modern script technologies and a compilation of powerful components, which are combinable with each other. Yootheme provide this free framework on GitHub. The integrated customizer helps you to create beautiful template styles with few clicks. Great CSS skills are not necessary for that. UIKit use also LESS, which is good for the website speed. You can use this framework, like Bootstrap, platform-independent under MIT License.