Thanks all. :)

I'm assuming if it was as easy as buying decent hardware it wouldn't be an issue, so presumably the number of people and/or size of venues make it either a logistical hassle or too expensive. I need to ask those questions and make sure I'm not misreading the actual problem, but also want to get an idea of feasibility first before I start asking questions.

The benefits of having devices connecting to a mesh (particularly if it's "download app and press button") is it means not having someone needing to spread large numbers of access points around thousands of square feet and multiple halls, all the while avoiding dead-spots and stuff.

If it needs Java then so be it. I'll wear gloves. :) Would definitely get someone else to handle an iOS port though.

FireChat uses Open Garden, which appears to be the sort of thing I'm looking for, but it's proprietary and their API is a link to an email address... :/

If the ease-of-use can get to plugging a [handful of] preconfigured RPis into wired networks and a simple app for all platforms, it could be pretty cool.

Sounds like there's a lot of research and coding to be done. What sustenance might you choose for such a task?

Er, tea and ginger nuts, probably. Why?

That's fine for a snack, but what if you needed something a little more substantial?

Two mugs of tea, a pack and a half of ginger nuts, the odd bourbon, strawberry milkshake, a malt loaf, and a mug of tea.

When the coding starts, add a mug of tea, a couple of chocolate biscuits, the rest of the ginger nuts, a bottle or two of cola, and a few chocolate-coated rice cakes.

So no Italian inspired, oven cooked open sandwiches?

Uh, what?! For research and coding? No way. No fucking way!

In what situations would you have a pizza?

Wow, you really are the other side of the curve.

I have no idea what that means. :-|