I've been using the Joomla! open-source content management system to build websites since 2009. I now use it exclusively, and here's why.
Web 1.0 is long gone
In the olden days, websites were built by writing HTML code, one page at a time, and uploading each page to the Web server. If you needed to make a change, you had to download one page at a time, change the code, and upload it again. If you didn't speak fluent HTML, you had to have special software like Adobe Dreamweaver that cost hundreds of dollars, and even that had a steep learning curve. For websites with dozens or hundreds of pages, it was very unwieldy to make a site-wide change.
Joomla is a CMS
In a nutshell, a content management system (CMS) is the engine that runs most modern websites. It uses a database to keep track of all the text, images, interactive features, and other building blocks of your site, and it assembles all those pieces in any way you choose. This makes your site very flexible and easy to change at will.
Joomla is a happy medium between simplicity and power
The three most popular content management systems today are Drupal, Joomla, and WordPress. Drupal is the most powerful, but also the most difficult to use. WordPress has the quickest learning curve, but has fewer advanced features. Joomla strikes a great balance between the two: it's quite easy to learn the basics, but it's still extremely powerful.
There's no need to have special software on your computer
If you're using a Web browser like Firefox, Internet Explorer, Chrome, or Safari right now, you already have all the tools you need. The Joomla software runs on the Web, not on your computer, so you'll just use your regular browser to go to your own site, and log in to make changes.
There's no need to be a nerd
Most of my clients learn the basics of editing their website text, adding images, and creating links in less than an hour! This means you can keep your site up-to-date without having to be a hardcore techie, and without having to pay your "Web guy" just to fix a typo.
Joomla is free and open-source
Those of us who use open-source software like to say, "It's free as in 'free speech' and free as in 'free beer.'" There's no big corporation that owns Joomla - it's freely available for anyone to use, and it's constantly being developed and improved by smart, collaborative people around the world. A price tag of $0 is quite a bargain for some extremely powerful software.
Joomla is extensible
Thousands of extensions are available to plug into Joomla to add functionality. Extensions are to Joomla as apps are to a smartphone. It's easy to install a calendar of events, slideshow, image gallery, email contact form, even a full-fledged shopping cart system - almost anything you can imagine. Best of all, many extensions are free or low-cost.