Document similar tools and proofs of concepts

There are a lot of projects in PHP that have some code that represents operations entities like sites and servers.

Let's collect as many of these as possible in a document so we can make sure to learn as many lessons from the past as possible.

These projects have code that represents sites, servers, or tasks.

1. Hosting/provision modules
2. Drush
3. DSD module
4. Cloud module
5. Aegir 4 prototype.
6. Terra CLI
7. Director CLI
8. More TBD.

We should analyze these and use anything that makes sense.