ACRL 2019 used the platform ipostersessions.com for both their in-person posters and to make the materials available afterwards. I don’t know anything on the tech or pricing side. Our head of instruction attended the conference then shared links to select posters for discussion among all our instruction librarians.
Here’s an example:
https://acrl2019-acrl.ipostersessions.com/default.aspx?s=9E-BE-00-CC-8D-DA-2C-F2-AD-6A-D5-9B-6C-43-1F-BD
This deals with some of the technology side, but I would definitely want an interactive component, since a key benefit of poster sessions is to foster conversation with the presenters.