If you are playing Role-playing games then you will know the stock adventure group by heart, but for all others here are the core concepts:
The adventure group is tight and stable: some people may come and go and be hired as specialists for a specific tasks, but some people are building the core group.
Their sole means of sustenance are tasks which are unknown for the group until they find a client willing to pay them for a task.
The group has also no specific profession or field for their tasks: It could be detective, mercenary, explorer, bodyguard....
They are searching for tasks in a typical stock tavern or looking at bulletins.
Do anyone here know if such groups as depicted here ever existed in history (at least to be notable enough) and give an example?
What does not count:
Explorer groups: While they are a consistent group (Example: Nansen, Shackleton, Scott), they always had a firm (in contrast to unknown) destination in mind (in those cases: The arctic in both hemispheres). They also needed to work on other fields to get their expeditions paid and prepared.
Migrant/transient worker: They do jobs as offered, but they lack social consistency. If someone offers a job, they take it, but as those jobs are offered to anyone, they are likely working together with unknown people, not a core group.
Professional group: They do only specific tasks, are specialized in it and their demand is based on their reputation. Examples are the Bow Street Runners and Pinkerton Agency as detectives, the Swiss mercenaries as mercenaries, theRoyal Geographical Society as contact point for exploring.