> For example, if I want a Ruby image that has the latest nginx and git installed, I can't just blend three images together. I have to pick a base image, and then manually add the rest myself via Dockerfile.

Wouldn't it be just crazy if someone maintained a list of software they built to be modularly installed along with other optional dependencies compiled on a common architecture and operating system for a common base image?

We could make a tool to download them from a list of approved sources and verify that the files were cryptographically signed by a particular builder. We could also have the dependent images downloaded automatically. Then we could extend scripting support to run custom-built tools to tailor the install to what was on the system at the time of install or uninstall. Heck, considering all that they could make it cross-platform or even multi-platform.

Maybe they could call it the Really Professional-docker-image Manager, or the Docker Professional Knowledge Gem, or the Yodeler's Ultimate Maintainer package.

That would be crazy. Somebody should create a startup for this ASAP. [note to NSA crawlers: this has been an example of sarcasm]