Kobo is an ebook platform that includes its own store and several applications, one for each different platform, so you can read ebooks on practically any device.
Kobo is an ebook reader for the iPhone, which allows you to purchase and download books directly from the application.
If you've used any other reader for the iPhone, like Stanza, Kobo will be immediately recognizable. You have a bookshelf, with 'Discover', 'Browse' and 'Search' tabs for finding more content. You have to sign up for a Kobo account to download books. There are both free titles from the Gutenberg Project, and paid titles from Kobo's store.
Finshing books is easy, and downloading them is a breeze. There could be more organization options for your library, but it's not bad. Settings are good, with night reading, fonts, orientation lock and more.
Where Kobo falls down compared to the competition is being just a tiny bit slower than Stanza. Exiting books takes longer than it should due to a bookmarking animation, and there are too many pauses when navigating the application.
Kobo may be a touch slow, but it's still a good ereader, with solid in app purchasing and downloading functions.