GAL are simple programmable logic devices. The classic devices as GAL22V10 have been replaced by ATF22V10 devices from Microchip that are mostly compatible.

There is galasm from https://github.com/daveho/GALasm and many other forks. Go in the src directory and run make to have a binary.

Take an example file and run it as galasm <name>.pld to create a <name>.jed to be used on the chip programmer