Top 3 cold-storage open source projects

Cold store small files on paper as QR codes -- PGP keys, Bitcoin keys, Tox keys or any other small files in general.

gwallet is a minimalistic and pragmatist opensource lightweight crossplatform brainwallet for people that want to hold the most important cryptocurrencies in the same application with ease and peace of mind

Bitcoin Paper Key generator - using a thermal USB printer and a basic linux box (like a Rrasp. PI) - Paper Wallet Generator