TL;DR
You can use, modify, and redistribute the Appstrate core for any purpose, including commercial.
You must preserve copyright notices and state changes.
Full text
Apache License 2.0 — https://www.apache.org/licenses/LICENSE-2.0
What it covers
Everything in github.com/appstrate/appstrate except content explicitly marked otherwise.
What it doesn't cover
Appstrate Cloud (proprietary hosted service)
The Enterprise module (proprietary, commercial license)
Partner certifications and the Appstrate logo (trademark)