I am back home after attending MerbCamp in San Diego last weekend. Merb is sort of like a micro-kernel architecture version of Rails: a small core with many plugins (and also complete "slice" mini-apps) that (hopefully) do not depend on each other. The idea is that you only add in what you need. Right now is probably not the time to try Merb for the first time: the developers are working right now to release version 1.0 RC1 (with version 1.0 to follow as quickly as possible). I am currently using Merb 0.9.9 and I am not going to update until I can do a "gem update merb" to move up to the 1.0 APIs. As announced at MerbCamp, the developers want to stabilize the APIs for version 1.0 and then continually work with minor 1.x releases for about one year, then release 2.0 that is likely to not be very backwards compatible with 1.0. Also, 1.x releases will be backwards compatible with 1.0 but not necessarily other 1.y releases. I think that this is a good plan, and matches the way I have used Rails for the last three years: I tend to freeze individual projects against a specific version of Rails, and only do security updates. I plan on using Merb for a semantic web project, and I will probably just stick with 1.0 and not follow the API changes during the 1.x path towards 2.0.