There are, you have two choices, small cruise ships or cruise yachts. Although a cruise yacht, which is different from charting a yacht, is more expensive that a cruise ship. On a cruise yacht you have more personal service, possibly more and exotic ports and a better overall experience.
A small cruise ships would be like Royal Caribbean's Monarch of the Seas, which holds 2,744 passengers plus crew.
Seabourn has large yachts, which only carry, at the most, 450 passengers and as little as 208.