We point out free and bargain Non-Fiction titles to each other. Please don't post any self-published books*, and please do a search before posting to avoid duplicates.
In case no retailer is specifically mentioned in a post, it is safe to assume it's for Amazon US.
Be aware that many freebies are only free for a day, so grab them fast!
*Unless you have read them yourself, think they are excellent, and you're not connected to the author in any way.
Last year's thread.