This is a programmer for PIC microcontrollers I built a while ago.

parallel_port_programmer: This is the first programmer I built.
It uses a 3rd party library called DlPortIo that allows user space programmers 
to execute IN/OUT instructions.  It bit bangs data over the parallel port.
It is difficult to get microsecond accurate timing, so I ended up using fairly
large granularity delays.  As a result, it was really slow.

serial_port_programmer: This uses a PIC to drive the programming lines,
so a programmer is required to bootstrap it.  The programmer PIC communicates
with the host computer using a serial port.  I prototyped the first version
on a piece of perf board with point-to-point connections.  The schematic
is captured in serial-programmer.sch. I also design a version that would use
a USB-to-serial converter and was bus powered, but never built it.