Hello Fokhwar,
Sofwatre testing means Checking whether the application/Production working as per the requirement or not. The requirement is given by the client.
Normaly, companies using Oen soorce tool rather than owned tools. Because It was tested and verified by the experts. As you are saying you are going to start a company, better you should go for open source tools. But before choosing tools, think about what exactly the requirement is. Because lot of tools like, Functional testing tool, Performance testing tool, Regression testing tools available. Source code is not important if you are going for Black box testing(Requirement based testing).
Thanks
Kiran Prasad R
Engineer QA