Both IO Star and Star San are from Five Star Chemicals
. Star San is a phosphoric acid based sanitizer. IO Star is an iodine based sanitizer designed to compete directly with Iodophor. Both are no-rinse when used at 1oz/5gal concentration.
I assume that IO Star is like Iodophor in that the solution doesn't last very long, so it can't be stored like dilute Star San.