making an arduino isp programmer to program big batches without computer

Has anyone ever tried to build a arduino device that can program a big batch of attiny's with a the same program without the need to have it hooked up to the computer?
is there a tutorial out there to do this or does anybody know of any code to do this?

Kind regards, Edward

I thought this was an interesting solution SparkFun came up with:

I'm not sure it quite meets your criteria of not being "hooked up to the computer", since the Raspberry Pi is a computer, but considering you can get a Raspberry Pi Zero for $5 + shipping, it's a reasonable solution. That link also contains discussion of the alternatives they tried.

The more traditional approach:

Also GitHub - WestfW/OptiLoader: Arduino sketch for burning new bootloaders and
GitHub - adafruit/Standalone-Arduino-AVR-ISP-programmer: A standalone programmer for mass-programming AVR chips