.app domains are available at Red Foot Hosting.
They even come with a free SSL Certificate (some restrictions apply).
The .app extension is a secure namespace, so you need HTTPS and a SSL certificate for your wesbsite to load on most browsers.
You .APP registration includes a free credit for our Standard SSL certificate. To use the SSL certificate on your website, you need to redeem and activate it on the My Products page. The SSL Certificate is free on the .APP domains for full duration and continues on as the domain renews.
The Standard SSL certificate will remain free of charge and eligible for support only if used with your active .APP domain. Please do not use this SSL certificate with another domain.