LibriVox is nice for some things, but almost every book I've tried to listen to from there had untrained amateurish narrators and editors with poor recording quality. I find them pretty hard to listen to compared to professionally produced books. IMO, a much better alternative if you're looking for free audiobooks is your local lending library. In the US you can often access library audiobook collections on your phone or computer with OverDrive.
Hoopla is another good one for books, music... Kanopy has a broad selection of movies too. All paid for by your tax dollars (not free!) so be sure and take advantage.