If you were going to write a vertical market C# / WinForms / SQL Server application and needed an accounting "engine" for it, what software package would you chose ?

By vertical market, I mean the application is intended to solve a particular set of business problems, not be a generic accounting application. Thus the value add of the program is the 70% of non-accounting related functionality present in the finished product. The 30% of accounting functionality is merely to enable the basic accounting needs of the business.

I said all that to lead up to this: The accounting engine needs to be a royalty-free runtime license and not super expensive. I've found a couple C#/SQL Server accounting apps that can be had with source code and a royalty free run time for $150k+ and that would be fine for greenfield development funded by a large bankroll, but for smaller apps, that sort of capital outlay isn't feasible. Something along the lines of $5k to $15k for a royalty-free runtime would be more reasonable. Open-source would be even better.

By accounting engine, I mean something that takes care of at a minimum:

• General
• Ledger
• Invoices
• Statements
• Accounts Receivable
• Payments / Credits

Basically, an accounting engine should be something that lets the developer concentrate on the value added (industry specific business best practices / processes) part of the solution and not have to worry about how to implement the low level details of a double entry accounting system.

Ideally, the accounting engine would be something that is licensed on a royalty free run-time basis.

Suggestions, please ?