In case someone is wondering about availability:

https://www.registry.google/

Here are the important dates to be aware of in 2018:

Mar 29 - May 1: Trademark holders can register .app domains (known as the "Sunrise" period).

May 1 - May 8: Anyone can register available .app domains for an extra fee (known as the "Early Access" period).

May 8 and onwards: Anyone can register available .app domains (known as “General Availability").