Ultrastudio.org is a curated collection of interactive visualizations (mostly Java) that can be easily invoked from another E-learning websites by just planing a link. It started as the initiative to collect the open source (mostly GPL) visualizations that were written during the first raise of Java applets; most of them are freely available on the web but need a developer attention before they can be efficiently used.
The project team collects, reviews and usually fixes such applets, also updating them to the recent Java standard and adding capability of launching them through Java Web Start. Java Web Start application can be launched in separate frame just by following web start link; such links can be easily added to any E-learning website, extending its capabilities. When using such links, it is required to mention on your project that the visualization is part of Ultrastudio.org project, providing also a link.
The project currently hosts over 100 different visualizations in mathematics, physics, bioinformatics, programming algorithms and other areas. Most of them are open source; if preferred, open source applications can be easily recognized by reading the project review and description pages (several professors insisted on bi-lateral agreement "permission granted to use in Ultrastudio.org project without restrictions"). For all applications (without any exclusion) the source code is available on the site, allowing license checks and independent reviewing. While every care is done, it is still a responsibility of the teacher to check if the visualization is suitable for one's course.
Most of applications also have associated short articles, explaining, what it is shown. These are freely editable, they content is available under the terms of CC-BY-SA and can also be reused under the terms of this license.