Keil was founded in 1982 by Günter and Reinhard Keil, initially as a German GbR. In April 1985 the company was converted to Keil Elektronik GmbH to market add-on products for the development tools provided by many of the silicon vendors. Keil implemented the first C compiler designed from the ground-up specifically for the 8051 microcontroller.
Keil provides a broad range of development tools like ANSI C compilermacro assemblersdebuggers and simulators, linkersIDE, library managers, real-time operating systems and evaluation boards for Intel 8051, Intel MCS-251ARM, and XC16x/C16x/ST10 families.

You can watch the installation guide from this video