Zoner Callisto is the only software that can save ZMF format, so there are not really any alternatives when it comes to saving .zmf files.
Using the Insert option, you can import JPEG files into Zoner Callisto as objects to a new or existing document. The software supports a wide variety of raster file types for such exports, but it always exports them as objects because its primary focus is on vector graphics.
Updated: February 8, 2024