In Circuit Pogo Programmer for the ESP12 modules for when your designing a board and you have no room for ICSP headers. It uses the 2mm pitch through hole on the ESP12 modules to program them.

You can get all the parts from Digikey and Sparkfun. Use the image file below to etch the board or you can get it from OSHPark: https://oshpark.com/projects/h64odUL8