I use Excel with multiple sheets, some sheets are linked for costs, some are just for notes. I like to be able to configure the sheets and calculations, and amend them myself if/when needed.
The main purpose is to track cost of feeds and egg sales to see how far I am out of pocket. But only a dozen or so birds over wintered and I don't sell the the general public or claim any of it on my taxes....just a hobby that mostly pays for itself.
I use zipties from when they go from bator to brooder, right leg/left leg for year of hatch and various color combos for other notables....there's a sheet(s) for those too.