s51dude is an In-System programming tool specifically designed to be
used with the usbtinyisp board and the Atmel's 8051 family of micrcontrollers.

This program is intended to cover the need of the 8051 developer who wants
to program the devices with computers without parallel or serial port. The
only alternative left is to use the USB port.
That is when you will need s51dude.

It's written in C.