Csound is a sound and music computing system which was originally developed by Barry Vercoe in 1985 at MIT Media Lab. Since the 90s, it has been developed by a group of core developers. A wider community of volunteers contribute examples, documentation, articles, and takes part in the Csound development with bug reports, feature requests and discussions with the core development team.
Although Csound has a strong tradition as a tool for composing electro-acoustic pieces, it is used by composers and musicians for any kind of music that can be made with the help of the computer. Csound has traditionally being used in a non-interactive score driven context, but nowadays it is mostly used in in a real-time context. Csound can run on a host of different platforms including all major operating systems as well as Android and iOS. Csound can also be called through other programming languages such as Python, Lua, C/C++, Java, etc.
One of the main principles in Csound development is to guarantee backwards compatibility. You can still render a Csound source file from 1986 on the latest Csound release, and you should be able to render a file written today with the latest Csound in 2036.
See, what others do with Csound:
Projects Using Csound
Music by Csounders