I thought context-free grammars seemed like the perfect way to think about some kind of game about making spells or potions or something, where you represent nonterminals as slots to be filled with other potion ingredients or runes or things like that.

That's not what this game is. I didn't have a clear idea of what I wanted the game to be, so I made the base system of defining a grammar and letting the player apply the productions to a string. While testing that out, it turned out to be pretty fun to design puzzles, which was enough for me, so I just kept that system as-is and made a more abstract puzzle game around it.

You can find it here.