Recs.
Updated
SpecsUpdate
Pros
Pro Supports HTTP streaming
HTTP Streaming is a technique that keeps a connection between the web server and the web client constantly open. When the server has new information, it's immediately pushed to the client.
This technique is used to considerably increase loading times, because using HTTP Streaming the web app can start rendering parts of the view that do not require any complicated calculations (for example CSS files) immediately.
But to use HTTP Streaming in a Ruby app you need a template engine that supports it, fortunately Slim fully supports HTTP Streaming.
Cons
Recommendations
Comments
Flagged Pros + Cons
Con Very little consistency among different versions
There have been quite some changes that break the compatibility between Slim 2 and Slim 3. Even if you learned how to work with the Slim 2, you will find that Slim 3 requires re-training.
Con Dependency injection is too weak
It is not really dependency injection, but just a configurable container.
Con Too minimal
While it's true that Slim is a microframework, it's still too minimal. When used for throwaway projects or simple prototypes, it's perfect. But in the long run, it becomes less and less useful and you end up in implementing a full custom framework in trying to tackle all the missing features.