This is one of our favourite distributions here at Symsys, because its extremely functional, quite easy to learn and use and in general is an all-round good operating system. I wouldnt necessarily recommend it for new users though.
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Debian is one of the mainstream and most popular distributions out there. Its main target market is corporate desktops and Servers and it does very well in both fields. There are rumours out there, which do not do it justice, such as Debian is very hard to install, it isnt at all. The installer isnt very pretty, its mostly text based, however its functional and it finishes with a very good system installation, not leaving much to update or have to mess around with to get it working.