My TinyLoadr AVR shield was a time saver because it allowed me to easily set up one of my Arduinos as an AVR programmer. The problem though was that it still required me to use one of my Arduinos, which were all usually being used in various projects. Disconnecting and reprogramming one each time I wanted a programmer was a pain.
I decided to take a stab at making my own standalone USB AVR programmer. I figured that I could take my existing shield design and simply adapt it to use onboard programming circuitry instead of relying on an Arduino. Sure I could have just bought a dedicated Arduino for programming, but this seemed more fun.
The end result was the TinyLoadr AVR Programmer. I went through a few different versions including an AVR-based option at first, but I settled on a USBtinyISP-based design as it was well supported by the community already and was very reliable, and components were much cheaper. I also opted for surface-mount instead of through-hole components to save board space.
Like the last generation TinyLoadr AVR Shield it uses multiplexers to route programming signals and power to various pins on the single ZIF socket, allowing it to program a range of ATtiny and ATmega AVR microcontrollers by simply changing the onboard jumper. It also has 10 and 6-pin ICSP headers to allow programming AVR-based target boards with those connections.