.app registrars, requirements and history
The addresses of every website on the Internet share one thing in common, no matter how different they might be in terms of content, scale, and popularity: They all require and use some derivative of the Top-Level Domain (TLD). This has led to some interesting phenomenons, specifically the "domain hack", wherein a TLD is used in a play on words.
One such Top-Level Domain is the newly-introduced .app domain. In today's day and age, apps - short for applications - are the hot item. They exist for work, for play, and for everything in between. As such, the .app domain is a necessity. In that the .app TLD is still under review (among others), there are no existing domains with this extension. It is, however, slated to join the existing pool of gTLDs, otherwise known as "generic Top-Level Domains", and there are already murmurs of domain hacking from the speculation crowd.
As far as a foundation / first-use date, the .app domain may be expected to appear, barring incident, sometime in 2013. It will likely be run under the auspices of the International Corporation for Assigned Names and Numbers (ICANN). Additionally, though it is logical to assume that this TLD is meant for use with apps and related phenomena, there are no special regulations or constraints attached to it or its use at this time. Even so, it is likely that tablets, mobile phones, and similar portable non-computer devices will enjoy the lion's share of this newly-emergent market in Top-Level Domains.