Sorry for giving you infos you already had, in fact looks like you are around with OpenACS sincle way longer than me 😊
There are some web-based embeddable chats around that are FOSS and similar to the application you pointed me to. In general they require a jabber server to take care of the communication (e.g. https://prosody.im/). Integrating with an existing OpenACS website might be some effort, so I don't know exactly if rolling your own code or going for one of these is better or not.
One example of such products to give an idea:
[1] https://conversejs.org/
Ciao!
