A few additions:
B&N's DRM can actually be read by readers such as the JetBook Lite and Pandigital Novel which have licensed it, so it's not solely limited to B&N devices and apps. It's supposed to have been incorporated into the next generation of ADE so hypothetically all future ADE-supporting devices could use it, but so far none have really popped up.
Kobo also has a proprietary format for which no download option will show itself on the book description page. It'll only work on their devices and apps and is what you get when you sync your Kobo Desktop Reader to your account.
Fictionwise's eReader DRM-ed format is actually what B&N's name/credit-card based DRM is based upon (they bought Fictionwise to obtain it, and Mac users can still download their B&N books as eReader .pdb off the website). It used to be supported by a number of devices (Nook classic-not-colour still does it, and there are apps for various smartphones & palmtops) but is on the decline.
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