What's the difference between Minoxidil and Rogaine?

There is no significant difference between Rogaine and topical minoxidil. Rogaine is a brand name. Minoxidil is a generic name.

Rogaine is a brand name for minoxidil. Minoxidil can be purchased in varying strengths from 2% to 5% liquid or foam.  Minoxidil can be helpful in male/female pattern hair loss when used consistently and as directed (2 x per day) . It is best used as part of an overall program that attacks the problem from different angles. (Capillus 272)

Rogaine is a popular brand name. The generic drug is called minoxidil. Many companies make minoxidil. Rogaine is the only producer of the foam formulation right now. 

Rogaine is the name brand. Minoxidil is the generic form. They both work the absolute same. Generic is the more affordable option.

These are the same medications, Rogaine being a brand name for minoxidil made by Upjohn pharmaceuticals.