First, what services do you want to aggregate? There are some plugins already available for ExpressionEngine for things like Flickr and Twitter.
Originally Posted by Savitri
If you want more services, you can try to create your own. Most of these services are based off of and/or ouput RSS feeds of your activity, either through the frontend or through their API. So, the basic concept here would be to combine all of these feeds and then do whatever you want with them.
SimplePie is a script that I've used in the past that can easily combine multiple feeds. It might be a start. I've read some warnings about using it on a PHP 4 environment, though I think it still works on 4.3+.
I was a little intrigued by this idea, so I did some Googling. In fact, I was more spot-on with my SimplePie suggestion, than I had initially anticipated. A lot of people
are using SimplePie for self-hosted lifestreams.
I think I might even give this thing a try. I'll post back with any results.