I also constantly ask myself this question
The way to download the book valid for 08/03/2019 is the @seekboo telegram
The project is moving purely on enthusiasm, no frills, but all the books I was looking for were found. Recommend
rutracker.org - I found many books that are not found anywhere else. It seems to have been blocked in Russia, but it is not difficult for an adequate person to bypass the block
I download from there, for free and in ePub format. Only some books have limited access. Basically, to books that are currently at the peak of popularity.
The bot in the @FreeBooksBot telegram looks for books of any format, and it searches for them on filibust, if I'm not mistaken, and does it quickly enough. Convenient enough.
Flibusta is still alive, however, you need to know how to bypass the block. The easiest way: http://proxy.flibusta.net/ For other methods, you can google it.