For those unaware, this project was previously called Lotus. I think this is being upvoted because it was mentioned in the recently popular solnic[0] blog post.
[0] http://solnic.eu/2016/05/22/my-time-with-rails-is-up.html
[0] http://solnic.eu/2016/05/22/my-time-with-rails-is-up.html
* Padrino (http://padrinorb.com) built on top of Sinatra
* Volt (http://voltframework.com) which allows you to write Ruby both in the backend and front-end
* Cuba (http://cuba.is) is a web microframework
* Roda (http://roda.jeremyevans.net) is also a microframework (both Cuba and Roda are like toolkits with very basic cored and a bunch of plugins distributed together with the framework)
We started at the same time, but unfortunately I never had the chance to play with Phoenix.