I've mentioned this before, but the "Y U NO HOST?" project is probably the easiest self-hosting solution out there, usable by just about any complete noob. It let's you roll out your own mailserver, cloud, and other hosted applications in literally a matter of minutes, and configures itself based on a handful of easy questions in the installation GUI. It's entirely GUI driven, LDAP based, and uses Debian as backline linux distro.
Right now, the project is in final beta stage for version 2, which looks a lot better and has more features than the already very successful version 1. Even though it's a beta, it's ready for deployment, I haven't seen any huge problems with it.
It's an ideal solution for private clouds and mail solutions, but also for small and medium enterprises.
You can download it (of course free and open source software!) at yunohost.org.
Looking to virtualize your yunohost server? Also running a database server or webserver next to it, that is also virtualized? Looking for an easy way to configure your virtual boxes with an easy to use and powerful open source libvirt-based solution? oVirt is the answer! The new version 3.4 offers a wide array of features, including full virtual container management based on libvirt, but also extensive storage management, whatever the configuration. Of course also free and open source software! It's very easy to install, it's a self-sufficient hypervizor like vSphere, but far less likely to generate the purple screen of death, and it uses no proprietary blobs, so it doesn't break with kernel updates. It's based on CentOS, but also part of Fedora and OpenSuSE standard repos, for those that don't want to install it as a standalone hypervizor.