I did a bunch more research on open source accounting / bookkeeping software and I was surprised I found a couple of projects I had never heard before. The problem with most of the open source accounting packages out there is that development on them has languished, or become too specialized. For example, the active project Compiere, is way more than just a basic accounting system, so the learning curve to customization is quite steep.
There are about a dozen projects that had significant work done on them only to stop being developed. Thankfully, most of the projects I'm looking at and researching were licensed under the GPL, so the efforts will not go wasted. At least the code can be examined, and at best it can be integrated into another GPL project. I'm not sure whether it could be integrated into an aGPL project, so I'm going to avoid that for now.
ALMOST WORKING: quickbooks to iif to qif to gnucashExporting DATA from Quickbooks
In Quickbooks, you can export "lists" to IIF files. IIF stands for Intuit Interchange format, which is a fancy way of saying it it a tab delimited document, aka tab separated value file (TSV). This makes it pretty east to transition to another application. One of the most important lists is the chart of accounts.