Mosaic
Fits images of any size into a fixed frame without cropping them. It picks the arrangement that leaves the least empty space, and you choose what to do with what's left.
Your files stay on this device — nothing is uploaded. Up to 20 files: images up to 30 MB and 50 MP (scaled down to 2048 px), and 10 videos up to 4 GB and 4K. Videos play muted: tap one to hear it (one at a time), double-tap it to watch it full screen. Memes load from imgflip.com only when you pick “Load random memes” from the arrow next to “Add files”.