Heif is a container file spec for images and image sequences. It may support a variety of high-efficiency image and video codecs, and making sure you have the right codecs installed can still be troublesome in non-Apple systems. With common codecs, it can store jpeg quality images in half the storage space, and also sequences of images, or images with higher color channel bit depths (10 bits/channel or more). So smaller and/or better.
Gimp includes some Heif support, as does Affinity Photo. Adobe, too, I think. But you may have to go codec hunting to make it work on any given system.