The WordPress Theme Customization API was released with WordPress 3.4, back in 2012. It promised developers a standardized way of adding rich options themes, and users a way of tweaking their website in a, well, user-friendly fashion.
For users, the front-end theme customizer allows you to quickly change the look of your site, and even get a live preview.
The success of this project is debatable but it is being improved upon and is gaining traction. It has been built on a solid foundation and there is no reason not to get started with it.