I think they’re very much on the decline these days, although they’re still around to an extent (there’s a rather prominent Swedenborgian Centre in London somewhere I seem to recall). During there heyday in the nineteenth century in Britain they built a significant number of rather grand gothic Churches, most of which are no longer under their ownership. I can’t say I’ve ever heard of them undertaking much in the way of proselytising, which may explain their decline.
Emanuel Swedenborg was an eighteenth-century Swedish scientist and philosopher (known to this day for first theorising the concept of neurons within the brain) who claimed to have experienced a series of visions on ‘the new Christian religion’. Although he never established an explicit religious group around his teachings, one grew up after his death. Essentially, it’s non-Trinitarian, very anti-Sola Fide (perhaps a reaction to the Swedish Lutheranism of the time), and teaches that a third ‘Last Judgement’ took place in 1757 (the previous two taking place at the time of Noah’s Flood and the Passion respectively). They also hold a rather unusual scriptural interpretation of the biblical account of creation, holding that it pertains to a process of internal rebirth within man.