Manufacturers, screen resolution, size, weight and lighting are some differences between Kindle and Nook. Both products are 7th generation, as of 2015, and have comparable bells and whistles, yet the Kindle offers better file support.
Nook supports PDF and EPUB, whereas Kindle supports Amazon's AZW and AZW3 books in addition to PDF, TXT, MOBI and PRC e-books. This flexibility allows readers to purchase e-books or obtain free e-books in any of these formats from vendors or parties other than Amazon.com, transmit the texts wirelessly to their Kindle devices via Whispernet or send them to Kindle by email.
Foxconn, a China-based company, manufactures the Kindle. Samsung manufactures Nook, but the company hasn't entirely managed to translate its track record with screen resolution on Galaxy phones to its e-book reader. Nook's resolution approaches 1024 by 758 pizels, whereas Kindle's is 1430 by 1080 pixels. The Nook is also roughly $100 cheaper than the latest Kindle.
Both the Nook and the Kindle have 6-inch screens, but the Kindle is markedly thinner and lighter than the Nook. A lighter e-book reader is presumably less cumbersome to hold and travel with. The Nook's silicon bumpers in multiple colors that provide function, aesthetic appeal and some protection. Kindle's key defining feature is its ambient light sensor that automatically adjusts its front light according to the surrounding light level.