fm Sytronics for 8051.
http://margo.student.utwente.nl/el/micros/80xx/clock.zip
http://margo.student.utwente.nl/el/micros/80xx/intrupts.zip
This program can create and evaluate computer circuits.
http://www.wssh.net/~wattsup/audio/eeng2.zip
http://margo.student.utwente.nl/el/micros/80xx/basic-52.zip
http://margo.student.utwente.nl/el/pc/586bug.zip
source codes.
http://margo.student.utwente.nl/el/ports/asyam.zip
with most of the common 8051 device info.
http://margo.student.utwente.nl/el/micros/80xx/tutor51.zip
program for easily accessing 8 output and 8 input pins in parallel port
http://homepages.together.net/~tking/parport.htm