There's a social reading platform called @bookwyrm which is an alternative to Amazon's Goodreads. BookWyrm is part of the Fediverse, and BookWyrm accounts can be followed from Mastodon etc. You can find out more at:
They are currently trying to get BookWyrm translated into more languages, so that more readers can use it. If you speak a language other than English, you can help translate at:
PixelFed uses the same federation protocol as Mastodon, which means Mastodon users can follow people on PixelFed and vice versa. You can try following a PixelFed account right now such as @Iancylkowski or @JoseMel or @connyduck
You can use PixelFed through a web browser, and there are also free open Android apps like @PixelDroid and FediLab (@apps).