Explode, a new service from Curverider (the British startup behind Elgg), is described as "a simple way to connect to all your friends regardless of what [social] network they belong to". Its essentially a meta-social network, the result of which is a widget that displays a list of all of a users friends, with links back to their designated profile page on an existing social network or blog. Users can also leave each other messages, regardless of what networks they belong to.
Although comparisons with Yahoo's MyBlogLog are inevitable, Explode isn't primarily intended as a way to turn an existing blog into a social network, nor as a way to monitor traffic. Instead, think of it as a loosely joined network that works on top of existing social networking sites and blogs, to allow a user of one site to 'befriend' and communicate with a user from another.
Curverider co-founder, Ben Werdmuller, says that Explode is very much a 'work in progress', and that they are already working on an API, and also have plans to add support for OpenID.
Update: More coverage over at TechCrunch