The Midjay is almost alone, Ketron has another modules, the XD3, and the new SD2, and each has different features, the Midjay can play MP3s, Wavs, SMFs with it's secuencer, styles, the XD3 is an arranger, so, only styles besides it's own tone generation, and the playback of SMFs, also the new SD2 is basically only a tone generator.
Korg makes only now the Triton Rack, and Yamaha makes the Motif ES rack, no arrangers, Roland besides the Fantom Rack, Varios, makes the Discover, SD20, VK8m, XV2020 and the MT90, none are arrangers.
THe previous models by Roland where the RA800, RA95, RA90, the Korgs I40m, and the I series I do not remember the models now.
I guess, in current ARRANGER module manufacturing, only Ketron.