An example of an Open Source Business
Naturally, everything we do is contributed back to the community. Many of our design changes have been accepted and merged into the main source tree for SQL-Ledger, but many have not. This is because some of our changes are not considered relevant to all deployments, and some are considered to be difficult to implement automatically in Windows environments. This means that for our work, we have a better platform to add even more features, and yet people who want a full-featured retail management environment based on Free/Open Source Software still cannot get it out of the box and have to come to us. Hence our costs are reduced, and we get help from across the community in maintaining some of our core features.
So if you are trying to start a business regarding Free/Open Source Software, it doesn't hurt to make an add-on for an existing software project that meets some specific need.