Matt Mullenweg and Mike Little developed WordPress as a fork of b2/cafelog. WordPress was Released on May 27, 2003 and was well-received by the community. The first version included a new admin interface, new templates, and generated XHTML 1.1 compliant templates. The following May version 1.2 was released and came with plugin architecture. Users were now able to write their own plugins and share them within the community. The adaption rate skyrocketed after this release. WordPress had a platform that rivaled their competitors. In February 2005 WordPress 1.5 released and had a whole new Theme System. This new system allowed users to set different templates throughout the different pages. It also allowed developers to place header, footer, and sidebars into their own separate files making applying site-wide changes a breeze. The developers continued to roll out update after update throughout the years offering tons of new features, tools, and settings. Over the last few years, the main focus has been improving the block editor. To date, 42.8% of the top 10 Million websites use WordPress!
WordPress.org is the open-source, self-hosted WordPress option. With WordPress.org the user installs the software onto their own computer or server. This version gives the greatest flexibility but also requires more back-end knowledge and learning. With this version the user must establish their own domain, hosting, and security.
WordPress.com is hosted on dedicated servers and is 'for-profit'. WordPress.com is owned by Automatic which has Matt Mullenweg as it's head. This version limits plug-in and themes for users but is much easier for beginners to get the hang of. There is an option to run a site through WordPress.com, but it requires hosting ads on your site and limits choices for domain name.
In summary, if you have knowledge of web coding and the ability to learn as you go, WordPress.org is a great option and a fraction of the price. Yes, it is technically free, but you will have to pay for domain and hosting at minimum to have your site up. WordPress.com is a great option for users who do not have back-end knowledge or the time/desire to learn it. It is a much more limited option, but still quite expansive and could have exactly what your site needs.