Software such as Plesk or cPanel provides a graphical interface and automation tools to make website hosting easy even for non-experts. It provides functionality for administrators, resellers, and end-users to control various aspects of a website and server administration through a browser.
cPanel is the most popular, most widely used, and probably a powerful software for managing websites or email accounts. However, it is not free, which is why many webmasters look for free cPanel alternatives.
Most of the software that I list in this guide are open source, which means that you can examine their code. You can even make changes you need to. They are all free, but some have limitations for commercial use.
I hope this introduction to web server configuration systems has bought some interest to you, as you can see, you can save money by using alternatives to cPanel. Paid solutions are also available such as Cloudron, Plesk, and ClusterCS with a little expenditure.