These I would hardly describe as casual as they are immersive and more than a little additive but on his recent visit His Bone of Ice introduced me to "The Room" and it's sequels. They may have been mentioned elsewhere in the Entertainment section but I don't recall seeing them.
These are pay apps, not freebies, but they are definitely worth it. If you have a medium to long haul flight coming up then definitely grab a couple or just do it anyway - you won't regret it but you may lose a weekend. Or two.
Stumbled across Dig It! over the weekend. Ads are annoying but a small fee gets rid of those. Game play is simple enough but it's pretty good at getting both the logical and lateral thinking sides of your brain going. Have to confess to being completely hooked.
Also I must get Monument Valley 2 at some point, especially as 3 is on its way soon.
Been playing 8 Ball Pool recently. Since the ceiling collapsed in the room that houses my real table, I can't use it. Different modes, and bets for different levels, you can play free, or make in-app purchases. Tournaments, or stand alone games if you're short on time.
It does make me miss playing the real thing though.