The development of Linux is one of the most prominent examples of free and open source software collaboration: the underlying source code may be used, modified, and distributed commercially or non-commercially by anyone under licenses such as the GNU General Public License.
Linux is completely free. It is possible that you will find some Linux distributions that offer "Premium" versions, that generally include more software or other features not offered in the free versions, but the price is nothing compared to mainstream operating systems. And the upgrade process afterwards is free once a donation is made. However, the most user-friendly and popular versions will not cost you a dime!
There are versions that offer paid support/engineering. Red Hat Enterprise Linux, and Oracle Enterprise Linux are two that work that way. Those are typically for corporate users and those that have the business requirement to have the support.
Linux offers speed, performance, stability, and reliability that rivals (or surpasses) that of commercial operating systems costing hundreds or thousands of dollars.Linux contains all the features required of modern desktop PCs, corporate file servers, firewalls, routers, and Internet servers.
Linux systems are by no means infallible, but one of their key advantages lies in the way account privileges are assigned. In Windows, users are generally given administrator access by default, which means they pretty much have access to everything on the system, even its most crucial parts. So, then, do viruses. With Linux, on the other hand, users do not usually have such "root" privileges; rather, they're typically given lower-level accounts. What that means is that even if a Linux system is compromised, the virus won't have the root access it would need to do damage system-wide; more likely, just the user's local files and programs would be affected.