The book that made me laugh the most came from there, though I see it's no longer published. However, it's still in my Smashwords Library (where you store books you download at the site).
As a reader, you can download books in any format and read them on a computer or on your ereader -- any brand of ereader.
As an author, I like Smashwords because I can load a book there and sell it on a number of sites. Back in 2010, I definitely didn't know how to self-publish. Smashwords' publications taught me much about ebook production. Its founder, Mark Coker, writes in an informal style, so learning was easier for me.
I don't do a lot of free books, since writing is much of my income. One is a short story called Tess and All Kinds. It's from the point of view of a child who has moved in with grandma, who manages a storage facility.
I can do coupons to make a book free, so if you see one you like, give a holler in the comments section.