Tiscali have this for their support and community forums (I was once a mod on there, which was how I got into vB in the first place).
Their login is ONLY by email though.
When the ran the 2.x series this worked fine. Since they upgraded to 3.0.7 they have made a right pigs ear of it and it rarely works 100%, they are talking of going back to normal login for the 3.5 upgrade, if they ever get round to doing it.
I presume this must have been some sort of custom hack as I never saw it over here.
http://www.tiscali.co.uk/forums