The Founders Edition cards are simply Nvidia's in-house designs for its graphics cards, as opposed to those designed by its partners. These are usually reference cards, meaning they run at stock clocks.
Briefly, for the RTX 20-series, Nvidia decided to offer Founders Editions with factory overclocks. These had made it a little difficult to compare cards, as Founders Edition cards give us a baseline for performance, but Nvidia has since returned to producing them as reference again.
Intel also offers something similar with its Limited Edition Arc Alchemist cards featuring its own in-house cooler design, as does AMD with its reference cards.