To echo what another commenter said, I feel like a lot of the suggested alternatives are missing the mark a bit in regards to understanding what Reddit actually is (a community of communities). It seems like a lot of the platforms that are popping up are more akin to being just a huge bucket full of posts with hashtags opposed to being a collection of communities. They are sort of missing out on capturing the community part.

Shameless plug, but that's been a focus of ours with the platform that I've been building (sociables.com). We are trying to create an all in one stop for people to create communities, and not just posts.

Here's an example of a community on the platform:

https://sociables.com/community/Sports/board/trending