Many home and office printers can't print on both sides by themselves. FlipStack fixes that from the macOS menu bar: drop a file, print the fronts, flip the stack once when asked, and the backs come out in the right order. No shuffling, no guesswork, half the paper. PDFs, photos (bit-exact, never recompressed), and Word/text documents. Real driver options for paper, quality, and page ranges. Fully local, Open source, MIT.