Rerun co-founder here. Rerun doesn’t have replay in the sense of you send messages in and can play back the same messages in the same order later. We have playback in the sense that you can play it back in the viewer. We also have apis for reading back data but its more focused on dataframe use cases rather than sending you back messages
They've since raised more funding recently, and have larger use cases in mind for robotics: https://rerun.io/blog/physical-ai-data
I've spoken with members of the team, and they're all great. Wouldn't hesitate to use the product / work with them anywhere.