[Podman] What are the main differences between Podman and Singularity? (Possible FAQ)

Regarding the email thread: "We are working on creating a FAQ for Podman" I'm curious about the question: What are the main differences between Podman and Singularity? I think in the academic world Singularity has become quite popular. The PhD students in my work place build the SIF (Singularity Image Format) file on their local computer and then copy it to the cluster with the scp command and run it there. (In some research HPC compute clusters they have installed Singularity) (Not so much of an answer but I tried to describe the situation where I get the question).