Bjud en okänd vän på middag (Invite a unknown friend for dinner) is the name of a facebook group for people living in or visiting Gothenburg, who wants to meet people over a bite to eat. The group is active periodically, but several dinners have been arranged.
First, send a request to become a member of the closed group and see or suggest upcoming dinners in the feed.
It is always free, but it might be nice to bring a small gift to the host.