I’ve just finished my first release of an open source project for
doing svn:externals -like actions/deployment with any combination of
subprojects managed under different source control management systems.
I have several projects, some of which are managed under subversion,
and some managed under git. What’s worse, is each project has several
subprojects (rails plugins, perhaps a vendor/rails), half of which are
managed under git the other half under svn.
I really miss using the svn:externals feature of subversion for
managing subprojects. svn:externals allowed me to have your
subprojects be managed by a different repository than your main
project. Doing a checkout/export automatically checks out/exports the
subprojects. Doing a status will show you if any modified files in
subprojects.
ext allows you to use this same workflow with any combination of
source control management systems.
I have written a tutorial for ext at http://nopugs.com/ext-tutorial
The source code is also available at
GitHub - azimux/externals: provides a svn:externals like workflow in an scm agnostic manner
It should be pretty easy to install and play with and is quite
feature-complete
This is my first ever attempt at contributing an open source project
to the community. Any advice/suggestions would be much appreciated 
I started this project out of necessity to get around the annoyances
of using git/svn together for managing and deplying projects with
subprojects, and think it could be really beneficial to other
programmers.
Thanks,
Miles