Looks interesting (as a writer - I don't read the genres of most of the free books). https://www.prolificworks.com/
prolific works is what used to be insta freebie... their give aways have some benefit in building your email list, but on the flip side you will attract a fair number of freebie leeches (those who will never buy and are only interested in freebies) personally I'd suggest its better to build your list organically from the back matter of your books, which is slower but generates a better qualityof subscriber
