Order Attributes

or search frequently asked questions:

How to get/output order attribute value via PHP code?
Is this plugin compatible with one step checkout extensions?
Does this extension add attributes to existing checkout steps or to custom ones?
Are dependent attributes supported by the module?
Can I use created attributes in order-related emails and documents?
Can I use Order Attributes only in one store in a multi-store configuration?
Can I use different order attributes in my multiple store views?
Can a created attribute be displayed on the Order Grid?
Does this Order Attributes module work with SOAP API v.2?