You can download any of the virtual machines in this project and fire them up in Oracle's VirtualBox (suggested) or VMWare's Player (or even QEMU if you don't mind extracting and converting some files).
It's a small and simple project aimed at attempting to present a single-file (in this case, using the OVA format which is simply a tar file with the OVF files inside) for the sole purpose of testing/using most major Operating Systems which are release/maintained under any Open Source License. There's often times no reason to have to go through the entire installation process if you're just tinkering around. While many Linux distributions do serve "Live" snapshots, this isn't aimed solely at Linux, and those run memory-backed, temporary file systems. That's fine for the purpose of a single boot, but that's not the goal of this project; having your data continue to persist while you try out one or multiple Operating Systems, and maintain the ability to move them from machine to machine as you see fit, IS the goal however.
With the proliferation of high-speed Internet, the amount of time spent downloading the ISO, and going through the installation process can ultimately be slower than simply downloading a single file (that is often only slightly larger than the installation media) and clicking a single "import" button. These are all ready to be imported and booted immediately, and once booted can be logged into, and are fully installed. They also have enough space to function as a desktop/server for most end-user's tasks, and of course as Virtual Machines their "hardware" can be modified as your needs dictate.
Further, there is an additional "Appliances" section, currently propagated by things like FreeNAS and pfSense, and expected to soon have a light-weight Quagga installation, and a full OpenStack install, ready out-of-the-box.
Common Operating System categories are listed below:
The login credentials follow the same guidelines for every Operating System*, specifically:
The "root" login will always be exactly that, "root".
Root Password: toor
The "username" will be the distribution you're running in lowercase, so if it's FreeBSD, the user's name is "freebsd".
User Password: nimda
*As usual, it is suggested that you change the passwords after your initial boot. Feel free to contact me with issues/questions.