We have 3 active D20 Campaigns (2 x FR, 1 x Wheel of Time).
And we had 2 Starwars and an additonal D&D Campaign, but they are not played often, and probably never again...
And than we still have a campaign Space Gothic, several Shadowrun Characters (I do not think in "campaign" terms here), Midgard 1880 and Torg (unfortunately only very seldom)...
I voted 3, since I only counted active D20 Campaigns...
(Every one in our group masters from time to time, and we play Saturday from 18:00 to open end / early morning)