We are very happy for companies (or individuals) to bundle ScummVM with their games, whether commercially (charging for the bundle is fine) or non-commercially.
This allows them to be played on modern platforms, often with bugfixes or enhancements, and we're delighted to have adventure games be more widely available and playable.
Some examples of existing companies selling their games using ScummVM include Revolution Software (e.g. the iOS re-release of Beneath a Steel Sky: Remastered and the Steam re-releases of Broken Sword), dotemu (e.g. Gobliiins on the iPhone), and gog.com (for many Windows adventure games).
However, if you intend to distribute ScummVM, then you must comply with our license, the GPL.
Most importantly: You must distribute the source code for the exact version of ScummVM you are using, whether you modified it or not, and any libraries/plugins you are using with it. You must make sure this source code corresponds *exactly* to the ScummVM binary you are distributing, and you should describe how you compiled the binary.
If it isn't possible for you to distribute the full source code (for example, if you are using Nintendo's Wii SDK, or linking against the SteamWorks DLL), you may not distribute your modified version of ScummVM at all! This is unfortunately not something we are able to negotiate about; due to the number of contributors involved, we are not able to change the licensing of ScummVM.
For releases where users are able to access the game files (such as on desktop computers), the easiest thing to do is simply to include the source code in a zip file along with your game, and note (for example in the README) that you're using ScummVM and the source code is included. You should be sure this includes a copy of the GPL license itself, and other documentation (such as our README and the AUTHORS/COPYRIGHT files).
Alternatively, and necessarily for releases on non-open systems such as the iOS App Store, the easiest thing to do is to provide a prominent notice (in your app description, ideally) that you are using ScummVM, that it is licensed under the GPL, and to provide a link to a page on your website where anyone can download the source code.
Other Licensing Requirements
You may not impose further restrictions (for example, via an EULA) on ScummVM itself. Please be careful about the license text you're using in installers, for example, and make it clear that any licensing restrictions don't apply to the ScummVM binary you're distributing.
For other details, you can read the GPL 2 itself here and the FSF's GPL FAQ 2 here.
You probably want to disable all other engines (build with --disable-all-engines and only --enable-engines=yourenginename), and also build with --enable-release (to build in release mode, rather than the standard development mode).
Please feel free to contact us if you'd like assistance or clarification.