Note: This is only a developer-level add-on for setting up one setting on your site. If you're looking for a more robust solution for managing multiple domains you own in a single concrete5 installation, you should take a look at the Multiple Domains add-on.
This add-on is no longer required in the newest concrete5 releases! This used to solve a problem in earlier versions.
These questions help you decide whether this add-on is for you or not:
Forget your frustration - Multi Url Site add-on to the rescue!
This add-on gives help to developers who need to configure the site to work in multiple urls. This is the case for example when you have different environments for development, testing and production.
Also, many times we've faced a situation when the actual url is not directing to the site yet and the site is working in an url like beta.site.com although it would run on the production server. So in this case the administrator would have to re-configure the site on the day that it goes "live". This can be sometimes quite annoying.
This add-on gives you the possibility to configure multiple url's (or if you want, all urls that point to your server) for your site. Setting REDIRECT_TO_BASE_URL to false is not sufficient many times because it does not redirect unwanted urls to correct location.
To have this package working, just comment out the BASE_URL setting in your site.php and check out the configuration section from the documentation of this package.