#OpenSource rewrites of classic game engines are amazing. #ScummVM , #OpenMW , #OpenRCT2 , #fheroes2 , #devilutionX are some of my favorites. The best way to not only a) preserve classic games, but also b) enhance them, c) port them to new operating systems, and d) turn them from proprietary software into just binary data read by an open source program.
I appreciate #GOG for not only hosting and selling no-DRM copies of these old games, but often bundling the open source engines officially.