It is a pleasure for us that you have run OnWorks, the free hosting provider to run your workstations online with OS like CentOS, Fedora, Ubuntu and Debian. OnWorks gives you multiple OS online. Among the most important are:

Ubuntu

Ubuntu is an open-source operating system (OS) based on the Debian GNU/Linux distribution. Ubuntu incorporates all the features of a Unix OS with an added customizable GUI, which makes it popular in universities and research organizations. Ubuntu is primarily designed to be used on personal computers, although a server editions does also exist.

Ubuntu was the first to the game of "user-friendly linux desktop". Although now there exist even more user-friendly Ubuntu-based distros like Linux Mint and Pinguy OS, Ubuntu was the pioneer and hence has become a brand and de-facto standard, pretty much like Microsoft. When compared with conventional Linux distros,Ubuntu has several advantages:
1.Easy install
2.Wubi ,ability to try it from within windows without partitioning
3.It derives from Debian which is a rock-solid distro with the biggest software repository.However, it improves on Debian by providing proprietary drivers,even more software through support of PPA's, a more user-friendly install and added visual polishing.This means that essentially all of Debian's strong points like big community support, the popular .deb formats everything works in Ubuntu.
4.Ubuntu, over time, has developed a big community of its own which is newbie-friendly and helpful in case you get stuck in any issue.
5.Canonical, the company behind Ubuntu, has the vision of taking Ubuntu to the mainstream.Hence,every move and design is made with this single focus,and their product,although not the best, is overall the best to get a person started with GNU/Linux.

Fedora

Fedora is a popular open source Linux-based operating system. Fedora is designed as a secure, general purpose operating system. The operating system is developed on a six-month release cycle, under the auspices of the Fedora Project. Fedora is sponsored by Red Hat.
It is based on Red Hat Linux. This was the father RPM-based distro who started it all. It debuted in 1995 and continued to be released until 2003, when the last release, RHL 9, signalled the death of RHL and the birth of the Fedora project.
Fedora started as Fedora Core and took over the RHL repositories and development lines. It is a community project, but it was sponsored by Red Hat from the start. We had 7 releases of Fedora Core, before the Core and Extra repositories of the system were merged, and it became the Fedora.

Debian

Debian is a Linux distribution that was first developed in 1993 by Ian Murdock, a then American university student. It is named after him and his then girlfriend, Debra Lynn (Deb- from Debra + Ian = Debian).
Linux distributions are operating systems that all share one, essential component, the Linux kernel. An operating system kernel (of which the Linux kernel is an example) is essentially a translator, it translates what your software wants to do (i.e. input/output requests) into instructions that your hardware can understand. The Linux kernel is the operating system kernel with the greatest number of developers and may support more processor architectures (not sure the NetBSD kernel may beat it here) than any other operating system kernel.
Debian is arguably the most successful Linux distribution of all time as it has more derivatives than any other: it has more developers than any other Linux distribution; it and its derivatives are the most popular distributions on the desktop, laptop and server, by far; and it is the second eldest continuously-maintained Linux distribution (after Slackware).

Further details can be found in the following links: