From the ALSA wiki
What is Linux?
Linux is an operating system ("OS") for PCs and other types of computer. Linux is "libre" software meaning its program design (source code) is freely available for anyone to use, copy, modify, sell, rent or publish. This makes Linux fundamentally different from the Microsoft Windows operating system, which does not give its users any of these freedoms. Several years ago Linux used to be quite difficult to use but there are now versions of Linux with easy-to-use graphical user interfaces and a huge amount of software ranging from office-productivity software to complex scientific software.
Linux uses the ALSA sound system to provide support for multimedia applications such as video players (mplayer, xine, ...), audio editors (Audacity, ...) and music programs (Rosegarden, MuSe,...). This Wiki has many pages about ALSA; please see the contents page at AlsaOpensrcOrg for an overview.
More information about Linux is available at Linux Online http://www.linux.org/.
Linux is a registered trademark of Linus Torvalds, Microsoft and Windows are registered trademarks of Microsoft Corporation.