technology recommendation for LAN Dashboard
Thank you everyone for your helpful answers!  I think they address most of the issues raised by the question.  But I think the key to the "final answer" (IMO) rests on the "multiple database" aspect.  Railsninja suggested a piece of software he used for a project to extend rails functionality in this manner - thank you for the link!  That could have been a possible solution - but it sounds like it was used for one project, and I worry about the testing since it is not a part of the mainstream Rails build.  
Then I found out that multi-db support is just around the corner for a Django core update (eta late August 2009).  So I think I am going to dive in to the project with Django.
I'm about to start a fairly large project for a mid-sized business
with a lot of integration with other systems (POS, accounting,
website, inventory, purchasing, etc.) The purpose of the system is to
try to reduce current data siloing and give employees role-based
access to the specific data entry and reports they need, as well as to
replace some manual and redundant business processes. The system needs
to be cross-platform (Windows/Linux), open source and is primarily for
LAN use.
My experience is mostly PHP/web/app development, but I have developed
a few LAN apps using Java/Servoy (like Filemaker).  I found Servoy to be very rapid and to easily make use of different data providers (DB products), but it's not open source, and any non-standard development is in Java/Swing (which is verbose and takes a lot of time).  
I'm interested in learning Python/Django or Ruby/Rails - but I'm not sure if these are the best solutions for building a mission critical data entry/reporting LAN app.  Is a web client/server really a good choice for this type of application?  
Thanks in advance for any tips/ advice.