Knowledge as in "knowledge sharing", "knowledge management", "knowledge worker" and "knowledge volunteer".

More aspects of the same in the PRODUCTIVITY 2.0 category.

20+ additions in this update, in italic.

5min - Upload, explore & share how to-videos ('videopedia')
7tipson - Browse & share tips
Able2know - Q&A
Allexperts - Q&A
Annotea - Create & share metadata
Annoyances - Q&A on Windows
Answerlytics - Q&A
Answers - Best answers to your questions
Answeru - Q&A on education
Askalibrarian - Q&A (Library of Congress)
Askeet - Ask & answer it
Askmehelpdesk - Provides answers & get tipped
Asktheworld - Q&A
Askville - Q&A by Amazon
Askvox - Write a question & hear the answer
Bitwine - Get or give video advice for a price
Blinkbits - Share knowledge
Brainkeeper - Capture, distribute & collaborate on corporate knowledge
Brainreactions - Participate in brainstorms & share ideas
Bubblus - Brainstorm together online
Circleup - Ask questions, get consolidated group's answer
Complore - Collaborate on research
Cooperationcommons - Knowledge base re cooperation & collective action
Cramster - Q&A
Dizzay - Q&A (instant answers through chat)
Duno - Q&A
Education - Q&A
Fluther - Q&A
Funadvice - Q&A
Gibeo - Share web annotations & content
Goodnotes - Bookmark, leave notes at & categorize web pages
Googlecoop - Share knowledge online
Grokker - Enterprise search & knowledge management
Growl - Semantic knowledge management
Grupthink - Explore & share topics & opinions
Guruza - Ask, or answer questions & get paid
Hanzoweb - Bookmark, tag & share knowledge online
Helenos - Semantic knowledge discovery
Helium - Buy, sell & trade knowledge
Hellup~ - Q&A
Hitchhikr* - Share knowledge & experiences on conferences
Hivelive - Post & share information
Hubpages - Share your genius
Ibridge - Aggregates early stage research & technologies
Illumio - Q&A
Instantnotes - Bookmark & leave notes at web pages
Instructables - Share what you make & how you made it
Intute - Validate & share academic information
Jabbits - Ask questions, watch answers
Jots - Information sharing
Kaboodle - Information sharing
Knowbrainers - Q&A
Knowbrainers - Q&A
Lookupahookup - Create or join an expert or experience group
Manyworlds - Explore business info reviewed & ranked by experts
Markthisdate~ - Publish & share events
Mousebrains - Thought starter for advertising creatives
Mozesmob - Mobile Q&A
Neighbor - Q&A (local)
Networkltd - Share research
Nownow - Ask a question, get three answers by email
Numinalmeme - Share & vote for ideas
Opinionaggregator - Q&A
Organizedwisdom - Publish & share your wisdom on health matters
Ownyourc* - Get help in making choices
Oyogi - Share Q&A
Postgenomic* - Share & rank life science knowledge
Qnalive - Microsoft's Q&A
Questionize - Q&A
Questionville - Q&A
Quomon - Q&A for IT issues
Rallypoint - Share knowledge
Reviewbasics* - Provide & get feedback on content & creative work
Riffs - Recommend, chat & share
Rootvaults* - Store, manage & share knowledge online
Sayoutloud - Post questions & issues, get answers or reactions
Shareyouropml - Share outlines, feed & taxonomy
Simplyexplained - Q&A
Skillsfeed - Share knowledge
Socialsaga* - Video Q&A
Sparkhive - Store & share thoughts, research, bookmarks
Spillr - Q&A
Squidoo - Share knowledge
Sutree - Knowledge sharing (thru video) community
Systemone - Enterprise knowledge sharing & management
Theanswerbank - Q&A
Thebeststuffintheworld - Submit, rank & share the best whatever
Theinjuries - Share knowledge & experiences about industrial injuries
Tipstrs - Publish & share tips on anything
Tracbac - Share, comment, revise & collaborate
Tutocle - Find, submit & share tutorials
Twocrowds - Share your predictions & have them assessed
Uclue - Q&A
Vatortv - Entrepreneurs share their ideas thru video
Videojug - Share know-how thru video
Visuarios - Publish & share how-to videos
Vitamint - Explore & share tips, and get paid
Wealthbasecamp - Share knowledge & ideas on wealth creation
Wechangetheworld - Submit, share & search ideas for a better world
Wehow - Profile & share your expertise
Whatshouldisay - Q&A
Wis - Q&A
Wisdomdb - Rate & share solutions to problems
Wondir - Share Q&A
Work - Publish & share articles on SME business
Yahooanswers - Share Q&A
Yedda - Q&A
Youtorials - Collaborate on tutorials
Zogix - Innovators' community

Italic = new. Update 061224, 070119, 070303, 070517, 060828.

No browser wars to be expected in this generation of the Web, although - strategically speaking - bringing a browser that would better cater to the needs of social media users could be a smart way to captivate audiences in the space of e.g. communities.

I am aware that there are some more browsers in the Mozilla/Firefox and Mac schools - AND numerous cool applications in the same tradition - that I don't report on in this or the other EVERYTHING 2.0 categories. But I'm simply too addicted to Opera's browser to look further into this. Any Mozilla/Firefox or Mac correspondents among the readership of this blog?

2 additions in this update, in italic.

3B - 3D web browser
Browse3D - 3D web browser
Browzar - Surf anonymously
Bubbles - Launch frequently used sites in your system tray from a light browser (download)
Camino - Mozilla power & Mac style browser
Ghostzilla - Browse the web within other apps
Heeii~ - Get context relevant suggestions for further reading while you browse
Maxthon - Tabbed browser, IE-compatible
Palary - Ajax browser
Piggy-bank - Semantic web browser (Firefox)
Psiphon* - Surf the web anonymously
Songbird* - Browse, download, manage & share all media
Spacetime* - 3D browser
Spherexplorer - 3D web browser
Swift - Safari-like browser for Windows (very alpha)
Swoot**~ - Build your own browser
T9space* - 10x faster browsing on your cell

Italic = new. Updated 061220, 070119, 070303, 070517, 070829.