Zotero is a free, fairly easy-to-use Firefox extension to help you collect, manage, and cite your research sources.
It's a good tool for doing literature review. for example (as a personal and light-weight alternative to wikis like this one). It also may be considered a personal learning environment, under the condition that the user finds an appropriate organization of the library...
- Automatic capture of citation information from web pages,
- Storage of PDFs, files, images, links, and whole web pages
- Flexible notetaking with autosave
- Search through your materials
- Playlist-like library organization.
- Homepage and download
Note: Editors like eXe are not extensions, but use the application framework of a web browser.