I miss the svn:externals feature when installing plugins that are managed under git. the -x switch used to do this.
I've released a gem called externals that manages subprojects in an scm agnostic way so that I can use an svn:externals-like workflow with git.
It's used like this: ext install git://github.com/rails/acts_as_list.git
This accomplishes the same thing as: script/plugin install -x git://github.com/rails/acts_as_list.git (if you pretend -x works with git)
I maintain a tutorial on how to use this gem to install ext and manage/deploy projects with subprojects managed in different SCMs at http://nopugs.com/ext-tutorial. I've been using it for my own projects and I find it really convenient.
The tutorial is rails-centric, though it can be used for any project type.
This is my first attempt at releasing a open source project to the community, any advice on how to get people interested in this project would be much appreciated.