Refs: Scenario Ideas

Genre and World-Building
For casual games, the first question a gaming group has to ask: what kind of world do we want to play in?

If this is a group that's used to coming together over D&D games, do they want to keep that sword and sorcery atmosphere or do they want to change it up?

Deciding the genre of the Campaign or Scenario will alter the flavor and color of the situations and tasks within it – and therefore what the players have to take into account when building characters. Note that there's little in contemporary atmosphere and objective that can't be adapted to any genre.

Creating Worlds from Scratch
The caveat to picking a world is the amount of work the chosen Ref is going to have as they build a campaign. Speculation provides some examples but nothing holds a candle to the depth and realism of a contemporary, if only because a literal world-full of real-life maps and locations already exist.

If the group decides to go with a genre look and feel, and the Ref doesn't have a world already set up in their head (or source material to adapt), consider giving an archetype and trope source, then having players kick in a few example locations and potential NPCs. The Ref may modify and adapt them, but if you've got a creative group, this is a great way to get buy-in on the overall atmosphere.

Adventure Hooks
The group may or may not have input on the exact premise for a scenario. A group of fantasy fans might have otherwise selected between two campaigns: break a curse in a jungle or stop the vampiric overlord of a terrorized land. It's a good idea to give at least that amount of consensus control to the Players, if only to establish some level of expectation management. That's a campaign synopses in the broadest strokes and find the balance between "no spoilers" and desired quest type.

For casual games, everything beyond that synopsis is part of the in-game reveal.

Most ready-made scenarios will be targeted towards a mixed group of adventurers. With some careful thought, it is possible to modify the situation of almost any one scenario into another, more appropriate one. If all else fails, create your own. This is time consuming, but can be a ton of fun.

Anything That Can Be Done Now Can Be Done There and Then
Think of any situation where a combat, recon, or street skill plays a pivotal part. PCs can be instigators of some situation, though this works best if  they expressed some interest previously. They can be victims of some situation, requiring clearing their name, hosing the pursuing bad guys, etc. They can buy into a ready-developing situation, like accepting a contract for one thing or another.
 * Specific military target
 * Assassination/protection
 * Extortion/defense
 * Theft/security
 * Illicit activities/investigation

Environment-Specific Challenges
The other route is a good companion to the timeless challenges. In this case, find situations and tasks that are particular to this genre and world. Sometimes, that just a matter of shifting vocabulary, but it's as much about the atmosphere and mindset in the flavor of the campaign.

For instance, assume that the players chose to go into a Hard Science Fiction world. What kind of concepts would work that are specialized to that environment? For characters, Hard SF is a high-intellectual option, requiring contact with unprecedented situations (at least for the characters).

These adventures use more obscure skills, often helping players to understand something totally foreign (and perhaps come up with a solution for a problem). If the Ref is stuck, I recommend borrowing ideas (you'll give 'em back, right?) from novels, TV shows, or movies. Likewise, tailor the type and frequency of conflict to match the Scenario.
 * Finding a cure for anything (for the characters or otherwise).
 * Repairing an old, alien, or decimated craft (for survival or profit).
 * Exploration (for cartography, diplmoacy, or profit).
 * Diplomacy. You represent (government, company, yourself). This is (first contact, negotiations, conflict resolution). Possible variables include: language, culture-beliefs (life style), contact history, technology levels, physical incompatibilites (water or methane sentients), and state of the society.