I don't know if all are aware of this (I haven't seen it mentioned here.....) but Endeavour Press issue (usually) 6 or (occasionally) 9 free books per week as epubs. Many (though not all) come well within the definition of the thread title.
Those that have d/l Endeavour books from this thread will know the sort of stuff available, but it seems that none of our regular contributors access this list on a regular basis.
All you need to do is to go here:
http://endeavourpress.com/
and the home page will invite you to sign up for the free newsletters (usually 2/3 per week in total)
Hope this helps someone: it's rare I don't d/l at least one per week........