It's a small search engine portal with a tagcloud (they call it a buzzcloud) that you can can customise, and then embed in a web page. What's really neat is that in customising a Swicki tag cloud you actually tune the search. I set one up on my other blog during the beta, which I focussed on SOA.
I found it easier to use (and install in my blog's template HTML) than Google's options - and by searching with a Swicki you add new tags to the cloud, and change the size of the tags based on the number of relevant queries and their usage. The idea is that the community that builds around a site or a blog builds and trains the search engine through their search actions. It's the logical extension of the collaborative search ranking engine that Eurekster have built.
Now, if they can get blog hosting services like LJ to support Swickis...
Oh, and they're based out of two of my favourite places.