Wikipedia Collaborations and Portals: One can find Science and Technology Collaborations from the page: http://en.wikipedia.org/wiki/Wikipedia:Collaborations . The Natural & Physical Sciences portals can be found: http://en.wikipedia.org/wiki/Portal:Contents/Portals#Natural_and_physical_sciences. All Science Portals in Wikipedia.
Science & Technology-related networks
2collab from Elsevier is a free collaboration tool for discussion, sharing and connecting with ones peers. It is quite well developed with many subject areas, and is connected to Scopus.
Nature Network: Connecting Scientists - Departments include: Blogs, New on the Network, Most Popular Tags, Most Active Groups, Most Active Forums, Recently Active People.
ResearchGATE is for scientists, built by scientists and supported by scientists all around the world. ResearchGATE has a video introduction on their home page.
SciSpace.net, "the collaborative network site designed for scientists by scientists"
"Pronetos exists to connect scholars and their institutions, facilitating collaboration and production of scholarly work. We offer a complementary set of products and services to help scholars collaborate, publish, and archive their works. We remove technological barriers so you can focus on what you know best - scholarship." from their "Welcome" They are building a repository, have a journals and a blog links. Modest gains so far and mainly in the humanities and social sciences.
Cestagi is a collaborative platform where you can share scientific contributions, enhance research partnership, inquire expertise in diverse fields, and track credentials and endeavors. On Cestagi com you may create your professional dynamic web page in minutes. When you login, you may modify your credentials at your convenience, including but not limited to your contact information, curriculum vitae, and research interests. Please use this opportunity to polish your professional image and keep your vitae accurate and up to date with our free online tool. (from an email)
Cestagi (ketaji) is a free software that you can use to create and maintain a biographical sketch site. The focus of the Cestagi project is to provide educators and young scholars innovative tools to manage and promote their unique credentials, enabling interdisciplinary communicative and collaborative efforts. (from their website)