This was my first Maya plugin and currently available to download for free. This is a constraint in which one transform can pull or push another transform a fixed distance between them. This gives the result of what you would see of a trailer being pulled behind a vehicle. You can also can create a series of constraints over multiple objects for a train type effect.
This plugin is free to use under the GPL v3 license.
Supported Maya versions and operating systems in this download:
Maya 2012 Windows 32 and 64
Maya 2013 Windows 32 and 64
Maya 2014 Windows 64, Mac OS X
Maya 2015 Windows 64, Mac OS X, Linux
Maya 2016 Windows 64, Mac OS X, Linux
Maya 2016 extension 2 Windows 64, Mac OS X, Linux
Maya 2017 Windows 64, Mac OS X, Linux
Python version for any version and OS (tested in 2012, 2013, and 2015)
Also available at GitHub:
git clone https://github.com/scottenglert/sePushPullConstraint.git