My current project is in Rails. Coming from a Symfony (PHP) and Django (Python) background, they both have excellent admin generators. Seems like this is missing in Rails.
The most common way to create a CRUD interface is to use Scaffold.
./script/generate scaffold_resource MyModel property:type property2:type2
This command would generate a CRUD interface for the model named MyModel (singular) with two properties. Properties is what's called columns in DB lingo. So you could have name:string age:integer active:boolean etc.