What is AVIF?

Built on the AV1 video codec, and the smallest of the widely-supported image formats by a clear margin - frequently half the size of a JPG that looks the same. It handles transparency and HDR. Being new is its only real drawback: plenty of software still won't open one.

What is PPM?

Uncompressed RGB behind a four-line text header - about as simple as an image format can be while still being one. Nobody ships PPM to users; it exists as the thing scripts and teaching code write when they'd rather not link an image library.