Kobo is an e-reader device as well as a publishing platform in the same way as Kindle (Direct Publishing) and iBooks. It apparently has up to 20% market share, though this is probably generous. That said, being originally a Canadian company taken over by a Japanese parent company, it does do well in these and other countries and has some good strategic partnerships which mean it IS a viable alternative to the monopolising Amazon (who are taking over the word – be warned). I think you can use the Kobo website to buy EPUB files for various devices, not just the Kobo.
My skeptical publishing imprint, Onus Books, and my original parent company (Ginger Prince Publications) now has presence with Kobo, and hopefully soon with iBooks.
Caleb Lack’s psychology books are not on this platform as he has some e-rights to them still, though I have just taken on his Kindle formats.
There is also some exciting news to come out soon with regards to new books to be published on Onus Books. Watch this space.