Hangouts, Meet and Chat are all the apps involving interaction in G Suite, but Google now offers overlapping functionality in these apps. This is because Meet and Chat will eventually replace Hangouts.
When can I use Hangouts?
When chatting with either a UiO user who does not have a Google Workplace account or with users outside of UiO. The users you are chatting with must have a Google account.
When can I use Meet and Chat?
If you want to arrange a meeting or a chat with a UiO user who has a Google Workplace at UiO account.
Limitations
UiO has not activated the Gmail or calendar function in Google Workplace. This is because Outlook Exchange is the preferred e-mail and calendar service at UiO. This means that services in the Hangouts menu, like Send e-mail or Schedule event can not be used.