Play all of the original Starcraft missions as either of the other two races.
The Secret Mission now playable as the two alternate races. Also featuring the Boot Camp Tutorial just in case you really care that much. To play, unzip the folders containing the maps [(Bonus) Dark Origin" and (Tutorial) Boot Camp] and place them in their campaigns folder within your Race Swapped Campaigns Folder. (Episode VI Queen of Blades for Dark Origin - Episode I Rebel Yell for Boot Camp) Or simply put them wherever you will remember to find them somewhere in your Starcraft Maps Folder.