There aren’t that many good examples of a free game turned into a paid product I can think of from the top of the head. Can think of plenty mods turned to paid games, sure. But free games? World of Goo was made from a free Experimental Gameplay Project title that simply had the same basic mechanics and looks. Super Win the Game is more of a successor to the free You Have to Win the Game. Only La-Mulana, Spelunky and maybe Eversion feel like actual “remakes”, which follow a more or less same structure as their original free counterpart but with updates. I suppose, Cave Story can somehow fit this list too. But point is – not that many I can think of, and, interestingly, almost all of them are somewhat metroidvania-ish.
Treasure Adventure Game is a free exploration-focused platformer with Zelda and Metroid influences that was released about 6 and a half years ago. I stumbled upon it due to it being featured on GOG and had a blast playing it 6 years ago. Then about a year later a remake was announced. Treasure Adventure World is a higher resolution, higher fidelity remake, with minor updates and several pacing changes, but overall unchanged design. For better and worse.
