Descent 1 and Descent 2 downloaded from GOG.COM.

Instructions couldn't be simpler.

1. Download & double-click .dmg file
2. Drag to Applications folder
3. Play!

A big thank you to the efforts from the GOG team.

If this works well for you, please support the developers by purchasing here: https://www.gog.com/game/descent_1_descent_2