I am writing a small ERP solution called Compass ERP, Its written in Ruby on Rails 4.1, If you know rails you can fairly install it on your servers and let people use it. Take a look at the screen shots here https://goblinrefuge.com/mediagoblin/u/mindaslab/collection/compass-erp/
Take a look at source code here https://github.com/mindaslab/erp
And here are the releases https://github.com/mindaslab/erp/releases
I would be happy if some one tries it out, gave me feedback so that I can improve the software.