Order Attributes

or search frequently asked questions:

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?
Does this Order Attributes module work with SOAP API v.2?
Can a created attribute be displayed on the Order Grid?
How to get/output order attribute value via PHP code?