Today is a Twitter conference, so Twitter is full of good stuff people have been saving up. Here's one: a "conversation prism" in bright happy colors showing a set of categories of tools, and how each one of them is occupied by some set of applications. Here's a mapping of each of them onto the set of tools that I am using to keep a2b3 loosely connected.
Sorry no links, didn't have time to hyperlink everything 
The Conversation Prism by Brian Solis and Jesse Thomas
Forums: Yahoo Groups
This is the biggest single tool I use for group continuity; it perhaps reflects my elderly nature that email is the first system rather than web-based forums or modern social networks. All I can say in my defense is that Usenet would have been better but it's really not available, and that I have 10 years of continuous use into Yahoo Groups and they haven't ruined it (yet).
Social networks: Facebook (intermittently)
Facebook will show up here frequently, if only because it's ubiquitous and because Ann Arbor is full of people who use it. My sense is that its group tools are way weaker than its personal tools and so it's best used as an adjunct to the main Yahoo group just so you can attach names to faces and so you can promote events.
"Interest and curated networks" (?): LinkedIn
I'm not sure about the category, but LinkedIn certainly qualifies as one ongoing conversation starting and continuing tool. Like Facebook, groups are second class objects in LinkedIn, and thus it's weak at building cohesion. On the plus side you don't have to pretend to be someone's pal to look up their resume.
Reviews and ratings: Yahoo Groups, Arborwiki
There are a bunch of national scale review sites, but nothing beats asking a good sized group of your peers for recommendations on everything from programming language libraries to pest control. To whatever extent possible, Arborwiki becomes the public long term storage for what would otherwise be something ephemeral and hard to retrieve through the Yahoo Groups search interface.
Location: none; I gave up on Plaxo when it creeped me out
Location-based mobile services are supposed to be the future of the social mobile web, but I lived through having my location visible on Plaxo and decided against living that way when people who knew where I was without me telling them didn't have the social clues not to be obvious that they were watching me. If I want to tell you where I am I'll be explicit about it on Twitter, or you can just wonder.
Video: whatever people use
There are a couple of filmmakers in the group, and I respect their judgement what to use for video. None of the video tools have strong group membership characteristics - or even particularly weak ones - so I treat them all pretty much interchangably as dumb hosting. (And no, I don't particular care if any given short video clip goes viral.)
Customer Service: Get Satisfaction, but it's not quite right
If a2b3 was a business it might need customer support, but it's not, and Get Satisfaction is just extra baggage. Tried it, it seemed to be functional, but not for the problem at hand.
Documents/Content: SlideShare seems to be a favorite
Those people who are giving presentations seem to have settled on SlideShare as a common denominator for hosting. The weekly lunches don't feature presentations so there's no natural synchronization around it as a tool, but it works as advertised.
Events: upcoming, Facebook events, in-person lunch w/announcements
Events are perhaps the hardest nut to crack, the thing that would make you spend all week promoting other people's work and the like. I have been telling people who don't have URLs for events to post them to upcoming; Facebook will tell you about more parties than you can manage to go to; and there's nothing like someone telling you about something around the table. The only way to really lick the events question is to have someone full time collecting them.
Music: One each of everything; I'm fond of how blip.fm twitters out songs
blip.fm is the closest thing to Napster that's out there; do a Twitter search for your favorite artist plus the word "blip" and you may be lucky enough to find a fellow fan and a track you can listen to. YouTube is also really good for songs - my 4 y/o calls it "picture music".
Wiki: Arborwiki, plus my own private Socialtext space
Arborwiki is the designated spot for dropping in information that deserves to live in a wiki; the "Birthday Deals" page there is the one universal attraction point around which much of the rest lives. I keep a Socialtext private wiki for my own personal memory augmentation tool, in part because it works awesomely on my Blackberry.
Livecasting video: haven't done it yet, not appropriate for lunch
If you want to join in to lunch, you don't want to watch it remotely; the space isn't set up for that. If and when I get to a place where regular live video streaming makes sense I'll use whatever the cool kids are using then.
Pictures: Flickr, Facebook photos
Once upon a time Flickr was a dynamic photo community, with dozens of awesome funny friendly creative people who you really wanted to share pictures with. Then everything grew up, people left for greener pastures, Yahoo acted stupid more than once, and my camera died. Now if I want to share a photo I'm more likely to put it on Facebook. I miss the old Flickr.
Social bookmarks: Delicious, plus whatever Les is working on
Once upon a time Delicious was a dynamic bookmark community, with dozens of awesome funny friendly smart people who you really wanted to share bookmarks with. Then everything group up, people left for greener pastures, Yahoo acted stupid more than once, and Twitter came along. Now if I want to share a link I think twice and either twitter it out or work it into a longer blog post. I just hope my 10,000 bookmarks stick around for a long time.
Comment and reputation: plenty of that around the lunch table
There's enough people who I care to converse with that I know by face and name that the level of comment-tracking promoted by blog tools seems irrelevant, for the most part, or at least too much work.
Crowdsourced content: arborwiki, a2geeks
Both arborwiki and a2geeks have enough of a wiki platform running for general and for technical info that if you need to crowdsource something there's a place to point people toward to edit things.
Collaboration: Google Spreadsheets (for football parking info)
If I need to collect a bunch of numbers from a bunch of people, Google Spreadsheets seems to do pretty well. I love wiki for private collaboration, but you have to be collaborating with people who love it too. Otherwise, printing things out and letting someone else wrestle with tracking changes in Microsoft Word is about as good as I get.
Blog platforms: Typepad
Someone else worries about it and I just hit "post".
Blogs/conversations: Google Blog Search is the best of a bad lot
It's hard to track conversations in blogs, in part because the blog vs comment distinction is weird. It's just as easy to do regular Google searches and put in teh word "blog" as an added qualifier.
Blog communities: mybloglog
I'm using this mostly for stats and to detect one-day spikes that mean that some seasonal post is current again or to notice when something is on fire.
Micromedia: Twitter
twitter, duh.
Twitter ecosystems: trying out Cotweet
I have a beta account; it's working pretty well to do future scheduled postings and to better track responses. Not sure yet if and how to open up the @a2b3 account to multiple posters but that's the next obvious thing.
SMS/Voice: Google Voice
It converts voice mail to text so that I don't have to listen to all of my voice mail. Still in closed beta.
Lifestreams: get a life! need some privacy sometime
Part of living a life is deciding what to broadcast to the Internet and what to keep quiet. I'm just as happy to be offline as online, and the idea that you should soulcast every last mood swing seems to be as unproductive as it gets
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After working my way through this, I realize what it's missing - all of these apps I write about are apps that work on a big screen. The real conversation prism also includes a parallel set of augmented reality supported by mobile devices, and that very well may include entirely new categories than above.