Hybrid core is a free WordPress theme framework developed by Justin Tadlock. It will help developers make their own parent themes by using a set of conventions and PHP scripts for handling common functionality within themes.
Hybrid core is not a WordPress theme. Its a Theme Framework. What does it means? As a theme user, you can not put the theme in your Themes Folder and start using it. It is for Theme developers to build solid parent themes quickly.
Let me clear it.. WordPress themes are a nice way of customizing the front end of your blog. However, every time a change was required, the user has to wither modify the theme or switch to a new theme. It became had not only for the blog owners but also for the theme developers, as with every iterations, they have to remember exactly what needs to be changed in the code.
Enter Parent Theme to the rescue. Parent Theme were developed to address this issue. So, the theme developers made a generic theme with all the features packed into a parent theme. Now all they need to do was to extend the Parent Theme into child theme to satisfy each of Blog owner’s needs.
Child theme are nothing more than CSS file plus functions.php file which basically tell the WordPress how to display the theme plus any small modifications. However, there were some modifications which were not possible by just editing the functions.php file / CSS code. Even if they were possible, the changes done made the child theme very complex. Another approach was to handle it by editing the Parent Theme file (which basically killed the whole purpose of using Child themes).
For Developers it became difficult to keep building more and more Parent Theme with new functionalities. To counter this limitations, Theme Framework like Hybrid core was developed. Hybrid Core helps theme developers to quickly build Parent Theme as per their requirements and then pack them with Child themes of your choice.
It is a win-win situation. Framework developers can concentrate on the Theme Framework, theme developers can focus on extending the Framework in their Parent Themes, while Blog Owners can restrict themselves to the Child Themes (which if deployed properly should consist of only basic CSS code and functions.php file only).
Thank you Justin.