Librivox is free and legal, it's part of the internet archive / sister website type thing (they accept donations).

Soulseek is p2p filesharing app, so... It may or may not be so legal depending on how you use it ¯⁠\⁠_⁠(⁠ツ⁠)⁠_⁠/⁠¯ 

 With Librivox one must note that not all books are in the public domain in the whole world.
They use books from the Gutenberg project, which follows US law.
A book can be in the public domain in some countries but not others.