Barnes & Noble has not done that well with their Nook ereader and tablet sales, certainly not compared to Kindle sales. Of course, like Amazon, they offer an app version for reading on other devices, like PCs, iPads, Android tablets, and phones. The Windows 8 version I have on my laptop is actually pretty nice, once you figure out that you have to right-click to get to the menus. Interestingly, Nook sales of my books have crept up lately, and they're now about the same (or sometimes better) than my Kindle sales, which was surprising in light of the reported recent bad Nook news.
Barnes & Noble now offers a nice direct-to-Nook self-publishing platform in Nook Press. One thing it offers is the ability to edit the epub file, and republish a corrected version if you need to. Amazon offers something similar, but only if you uploaded an HTML file, not if you uploaded a Kindle-formatted *.azw file. Some of my B&N books are actually coming from Smashwords, because before Nook Press, the B&N platform didn't offer much of an advantage. Ergo, only No Safe Haven, Tribes, and King of Trees are on the Nook Press platform itself; the others are being published to the Nook store via Smashwords, which lets you push your books to many vendors. And of course, The Sixth Discipline has to stay as a Smashwords book because that's why it can be free. Like Amazon's KDP platform, B&N's Nook Press won't let you make a book free forever. Smashwords does, and B&N and most other retailers make their price whatever the Smashwords price is, even if that price is zero cents.
The one self-publishing platform I have not tried is Kobo's Writing Life. My Kobo sales via Smashwords have never encouraged me to make the effort to check them out. But whether you use individual retailers' platforms or Smashwords, I would urge all self-published authors to consider carefully before sticking with any one platform exclusively, even Kindle. The more outlets you have, the better your chances are of finding readers, and that's why we're all in this game.