annas archive is very nice

https://open-slum.org/

All the best shadow libraries

fmhy dot net

Local library, best free source of ebooks I've found out there, and it's perfectly legal.

if you've got the spare time to wait for the open sign ups on myanonamouse, they've got an extremely extensive collection of rather rare ebooks.

if not, annasarchive and the sources on fmhy are very useful.

lots of useful posts above but

not sci fi so much but Project Gutenberg has lots of old stuff, by that I mean Dickens, Joseph Konrad etal

my gfs currently reading Wilde's "The Picture of Dorian Gray" from there and loves it.

https://www.gutenberg.org/

but for Sci Fi there's Wells etc

https://www.gutenberg.org/ebooks/search/?query=h.+g.+wells

and they do have a science fiction category

https://www.gutenberg.org/ebooks/bookshelf/638

Z-library has a 10/day limit, but is a neat source to find books.

the electronic library. for suggestions about titles, I usually browse the locus and the nebula prizes

If you use Soulseek, you could do a search for a generic word and then filter it to .epub files and see what it finds

Torrents are sometimes organized under an author's name for their collected works

Archive.org has a bunch of public domain/commons books in e-reader formats

You can use a caliber extension called DeDRM to remove the DRM from ebooks your local library provides. As a bonus having active members helps them secure funding to provide valuable community services.

That being said I don't browse for books, I decide I want to read X and then get bummed when my local library doesn't have it. The shadow library basically has everything, and yiu can see which instances are up at https://open-slum.org

MAM is great if you can get in

Baen free library. You want SciFi? Baen has DRM free books before amazon existed.

https://www.baen.com/allbooks/category/index/id/2012

Usenet via Evan Buss's Openbooks

It's not piracy but https://freeread.de/@RGLibrary/ERBurroughs/ERBurroughs.html