@elizabethtasker@mastodon.online This is not exactly what you‘re asking for, but I‘ll describe what our workshop is doing.
Tl;dr: Zoom and Mattermost.
Long version: We‘re a satellite to a conference which offers Zoom for on-stage presentations, but no platform for poster sessions. For on-stage Q&A remote participants can submit text questions via Zoom. As the vast majority of our presentations are posters, we also use on-stage slots for elevator pitch sessions, i.e. 60-second single-slide presentations of each poster, to give everyone some screen time. Remote posters hand in a prerecorded video for their pitch to avoid connection issues and setup overhead. The live poster sessions are then in-person only. However, we have a slack-like chat server (Mattermost) that everyone gets access to several days ahead of time and that we keep running at least a week until after the workshop. Each paper gets its own room, with prefilled links to paper and poster/slides. Remote poster presentations are done via chat and can be as synchronous or asynchronous as presenters and audience like. All attendees are encouraged to use the chat, but no dedicated session exists, as we have a packed schedule already and don’t trust conference wifi.
The result is a hybrid event that has a clear preference for on-site participation (which we communicate clearly) but does what we can to make remote participation still worthwhile for remote attendees.