There are some different alternatives to Steemit, but these two are the most used:

https://busy.org
Busy is my favorite choice, because of its clean UI and features. Furthermore an official mobile app will be released soon (as stated here: https://steemit.com/busy/@jm90mm/busy-is-taking-over-bsteem).

https://zappl.com
Zappl is another common alternative to Steemit. This platform aims to become a sort of STEEM based Twitter.