An email-powered website
This was an early experiment, and I'm pretty sure it ran my web site for a bit. I can't find any evidence of this now though.
Comments as content
You comment on other people's posts by replying to the notification emails. This would create a blog post on your own site which was linked from theirs.
The idea is to ensure everyone retains all the content they have written, and break down the unnecessary distinction between content and comments.
You create new content by sending an email. The emails that got sent out were also copied to a mailing list of your friends as a notification mechanism. The format was email-style, much like the later Markdown.
I underestimated how much editing I would want to do. There wasn't much point editing stuff where you'd made a mistake, and you could only do it on the web site anyway, whilst much of the actual action happened over email. The result was that I was loath to actually send the emails because I knew I'd have to go and fix them in the web site anyway. Still, Alistair gave it a go, for which props.
You couldn't easily invite comments from people who'd not been there from the beginning.
With everyone's comments as posts on their own blog, which could be anywhere, it was difficult to build comment threads.