The users and developers.
Since Linux is a collaborative development environment, everyone that has contributed to the project has usually written some of the documentation.
Members of the Linux Documentation Project. Individual package maintainers write manual pages for their software.
every one who likes to help linux
government
Mario Sevilla
By configuring the bootloader to use Windows as the default menu option instead of Linux. Refer to documentation on how to do this.
Many distributions have documentation or builtin graphical installation utilities.
The 'man' or the 'info' command have documentation about utilities and commands in the system.
Man (or manual) pages
If by "Linux software" you mean the Linux kernel, it is made up of code submitted by thousands of contributors from all around the world. Linus Torvalds (creater of Linux) is the one who has the final say on what makes it into the final operating system. If you meant applications that run on Linux, there are hundreds of thousands of organizations that write software for Linux. A lot of it can be found in the Ubuntu Software Center
Most screensavers on Linux are modules run by Xscreensaver: http://en.wikipedia.org/wiki/XScreenSaver I don't know exactly how to convert a program to a module, check the Xscreensaver documentation.
Var directory is a sub directory of the root directory, The system writes data during process of its operation.