I’m interested to know what you class as “casual” 
I run a casual 18+ Horde raiding guild on the joint realms of Lightbringer/Mazrigos. We raid twice a week, Wednesday and Friday 9.30pm to midnight server time.
We don’t have set raid teams, but instead work on a “first come, first served” basis for raid sign-ups.
We focus on Normal and Heroic raiding. We very occasionally dabble with Mythic, but prefer the flexibility of non-Mythic raiding.
We are looking for one or two more tanks to add to our number although can’t guarantee a tanking position for every single raid - generally most raiders are flexible though and can fulfil different roles should the need arise.
We aren’t a pure raiding guild, however - we have many members who either never raid, or raid infrequently. Lots of people have different interests in-game (and out, of course!) which means that we’re not a “dead” guild during non-raiding times.
We use Teamspeak for comms during guild raids, our own Discord, Website, Facebook and Twitter feed.
If you’d like to know more, head over to our realm post: