From the introduction:
Ba5ic is a fantasy role-playing game that encourages players to explore worlds of magic, monsters, and whatever else they can imagine. The game is designed to be rules-light, making improvisational, pick-up, and long-term play a breeze for beginner and veteran players alike.
The flexibility of these rules allows for all kinds of imaginative monsters and characters. Ever want to play a Sorcerer that couldn’t cast magic? Now you can.
Ba5ic is compatible with Dungeons & Dragons (5th Edition).