There are lots of free downloads at the internet archive, including lots of chess books. Not all of the books there are especially interesting, and some (e.g. all four entries of Soviet Chess by Wade) turn out not to be of chess at all, but it's still worth a browse. (HT: Tim Cianciola.)
One entry I found interesting and then amusing was Frank Marshall's Marshall's Chess Openings. Some things he says there look reasonable, and a lower club player can get some good general ideas from the book. On the other hand, it's pretty funny to read claims like 1.e4 e5 2.Nf3 Nc6 3.Bc4 Nf6 is slightly better for Black, or that Black's best defense to the Ruy is 3...f5.
At a deeper level, I found the book provocative. My first reaction, especially upon seeing such categorical remarks, was to laugh at how primitive opening theory was at the time - even considering that he was writing for the general public at a time when amateur play was far more casual. But then I thought about some of my games against average club players, and realized how thin their opening knowledge really is, too, most of the time; especially when they're not in a pet opening. (One memorable tournament occurred in 2004 when, incredibly, in 6 of my 7 games I had a significant advantage by move 6!) Maybe there's a place for such primitive books in chessplayers' libraries after all. They can outgrow them, and hopefully quickly, but maybe it's a place to start.