SixApart have launched a plugin for MovableType that offers a similar activity stream service to Facebook and Plaxo, but you get to host it.
The Action Streams plugin, like Facebook and Plaxo, pulls your data from other services and lists it on the page, for example blog posts, Flickr photos, Tweets and more. The plugin does rely on having MovableType installed, but is self hosted, meaning that you control the list, including privacy settings and data ownership.
The plugin can also be used to aggregate activity from a group as well as an individual, providing a portal or front page to groups of all sizes.
This is a good move from SixApart at a time where open standards and open access are quickly building momentum from being niche desires to mainstream wants. SixApart open sourced MovableType in December and it still has a long way to go to recapture its once dominant position as the blogging platform provider of choice, but plugins like this will certainly help them along the way.