It's hard enough to keep track of all the information you gather when you do your own research. Once you add others to the mix of searching, finding, and gathering resources for research, it is vital to both keep track of your own contribution and to decide as a group on a method for collecting books, articles, web resources and the like. This page lists some free tools especially good for harvesting information with a group.

This is an example spreadsheet that a group might use to communicate about sources of information they've found.  Open this spreadsheet, make yourself a copy, share with your collaborators.  Use it to list all works you intend to take action on (e.g., read, skim for sources, read for methodology, etc.).  Feel free to change the columns to match what your group needs.

Great for keeping notes and collection information -- especially images -- from the web. The main drawback is full sharing with a group. Only "Premium" members can have full group editing, but free members can share "view-only" access with group members to individual notes or whole notebooks.

Zotero is great for capturing web content and biblographic information about published documents, but it is not as robust as EndNote or Mendeley in features you'll want to use when culling and organizing what you've collected. Luckily, Zotero is good at exporting in formats that can be imported into EndNote and Mendeley.

EndNote's strengths are in ingesting citations and documents from journal and book databases and catalogs. There are options for collecting web content, but they're not as smooth as tools created for that purpose. You can use EndNote to search databases directly, too.

You can share your citations with group members, but not the documents.