SF was un initiative promoted by VPK. The goal was to gather a broad Swedish left and possibly form a "popular-socialist" party like SF in Denmark and Norway.. It was specially directed toward the leftist sectors of the social democracy. SF declared that they wanted SAP (the social democracy) and VPK to organize tecnical electoral collaboration ahead of the elections of 1968. The idea was that SAP and VPK should have run together as SF. But SAP declared that double membership of SAP and SF was impossible, and the social democrats that did not exit SF were expelled. The SF-project quickly died out after only one and a half year of existance.

Sources:
Arbetarmakt: Den svenska arbetarrörelsen och socialismen
Lundberg, Månsson, Welander: Demonstranter, 1970, Bokförlaget PAN/Norstedts, Stockholm