If you are a conventional web developer building your own websites with core frameworks of PHP or J2EE (or similar technologies), you would be interested to know what content management systems (CMS) are. You could have heard about the savings in time and effort these systems can help you to achieve. Let us discuss what these systems actually are and ways they can help.
What are content management systems?
Content management systems are frameworks that can be readily deployed in the form of web applications. You need not design the architecture from scratch. Moreover, these systems assume some common functions that are required across web applications. For example, theme management and menus management are some common functions that almost every website would require. Based on the assumptions, the developers of the content management systems work on the common functions and deliver them along with the core system. This means, you need not develop the assumed common functions once again from scratch.
How CMS can help you?
1. A CMS Can Save Development and Maintenance Effort
Just because you need not develop functions from scratch, you are going to save plenty of your valuable time. You could use the time saved in a more productive way. Moreover, maintenance of CMS systems is fairly simple. Generally, any CMS would have an administration section with links to settings pages of different functions/features. For example, if you wish to add a new menu item in the navigation bar, you could do so within minutes from the corresponding settings page. In case you had not used CMS, you would be working at least half an hour in building a new menu item and testing the same.
2. Most of the Content Management Systems are Free to Use
Though few CMS systems require a fee to download and install, most of the systems that are popular can be used without spending a penny. A common expectation among most open source programmers is that the systems they use must be economical. This expectation is perfectly met by popular free CMS like Drupal, Joomla etc.
3. Good Knowledge In CMS Development Assures Plenty of Jobs
If you get a chance to look through job sites, you would be amazed to see a whole lot of projects that specifically require developers with CMS knowledge. Hence, if you can learn a CMS and gain mastery in a year or two, you are in a great position to find plenty of jobs.

Many famous Content Management Systems are based on PHP. You may have a look at a list of popular php cms systems available. My other article may help you know how to learn CMS step by step.