I'm reading Steven J. Zaloga's book about the T-54/55 main battle tanks at the moment where he gives a detailed account of the 'Drozd', the worlds first active tank defence system. Described shortly it was an automatic system consisting of two launcher arrays, each with four launcher tubes and a radar sensor. The radar would aquire any missile or rocket moving at speeds between 70 and 700m/s, the computer would determine which projectile to launch at it and do so when the missile/rocket was 7m from the tank and destroy it ( it is described in detail in my book and I'll be happy to provide if anyone is interested ). It was a bit too complex and expensive for the Soviet Army at the time, but it did enter service with the Soviet Naval Infantry. Only 250 systems were produced though, and they were replaced by reactive armour in the late 1980's. It was also exported to China and an 'undisclosed Middle East client' ( wonder who that might have been? ). With the computer technology of today it would be possible to make a similar system much less cumbersome, not to say less expensive. I'm not aware of any similar systems in service today though.
Not all in service, but google for Arena, FCLAS, AWiSS etc. The Israelis and USA are working on a system that is capable of handling 4 simultaneous attacks from different directions (there's a very cheesy promo video floating about on the net, complete with CGI and smooth-PR talk over). Try DefenseUpdate (US spelling, all one word IIRC), an on-line magazine that has a special section on active defence systems). Arena is a Russian follow-on to Drozd, (as is Drozd 2), and has, apparently, been packaged with some French AFV exports.
