WordPress History
WordPress is a free and open source CMS that was released in 2003. The largest differences between it and its origin program, b2 Cafelog, at the time was an admin console and new templates. Just a year later, users could start customizing it with plugins. The popularity of WordPress did start in these early days as well, but it wasn't necessarily a result of its own improvements. Rather, there was a different blogging site the released new, heavily disliked terms, so people searched for an alternate site. The trademark was officially filed in 2006, and after that, the only thing to note is that it continues to be improved until today. An interesting way they do versioning is using jazz musicians, but at least they still have version numbers for those who don't want to memorize that list.
WordPress.org
WordPress.org, most importantly, contains the download for WordPress. However, there's much more to be seen on the site like news, hosting options, and community opportunities. Downloading WordPress isn't the end for that type of content though. Anything else you may need like themes and plugins can be browsed and downloaded. Finally, they have probably the most in-depth documentation I've ever seen. It's almost like Wikipedia with the amount of links within one page.
WordPress.com
WordPress.com does contain some similar content to .org like themes, plugins, and some documentation. However, the main purpose is to sell a WordPress hosting option. I'm not even sure if there's a place to download WordPress on the site, but I guess you might not need to if you're not the one hosting. After doing research on other CMS' for the assignment, this hosting option seems fairly cheap. They also provide the most tiers I've seen, which lessens the chance you need to pay for more than you need.
Summary
Overall, with the ease of getting into WordPress and the prices of the hosting options, I feel like WordPress could be the best CMS out there. I certainly didn't have a problem doing this week's setup assignment knowing nothing about WordPress and not as much about web development as I do software development.