International Online Unlimited is a financial institution featured in the HD Universe. The company is most likely involved in offering loans, as evidenced by a billboard located in South Bohan in Grand Theft Auto IV which says, among other things, "Helping you buy things you can't afford." Its name is presumably a reference to "IOU," a term which refers both to a document that acknowledges a debt owed, and is an abbreviation that phonetically matches the phrase "I owe you."
In GTA IV, its main headquarters are located on Rand Ave. & Applewhite St. in Alderney City, Alderney, and is one of the buildings that makes up Alderney City's skyline. Its design is based on the Newark Legal Center in Newark, New Jersey.