Open Source systems are jointly developed by some of their users and then licensed free of charge to companies in return for feedback and further development.
One advantage of this concept is that without any initial outlay for the software the only expenses are for implementation services which can then be sensibly budgetted.
As Open Source software is generally developed in parallel by an extended community of programmers, built on other Open Source components, it is often found to be of greater integrity than proprietary software developed and tested by a smaller compact team, because of that diversity.
Open Source software includes operating systems like Linux, general software components like MySql and Apache as well as end user programs for specific purposes and the successful OpenOffice which is an alternative to Microsoft Office.
As Open Source uses these components, which are by definition interchangeable for other Open Source alternatives, they actually achieve a higher level of integrity.