www.btcentral.org.uk/projects/centmin/
Does Rayburst do anything different (apart from different programming languages)?
Is there any reason why Bash scripts can't deliver the same result as Rayburst?
rayburst sets up a framework to allow for more customized installs. You can pick the various apps and services and the modularity of the build scripts/recipes handles the install of the configuration. Part of what takes place is figuring out the build dependencies (ex Rails depends on Ruby) which would otherwise have to be hardcoded in a bash script.