Surfactants are substances which have a lot of utility and many different applications, especially in the area of cleaning. A surfactant has the useful property of being able to reduce water's surface tension even at fairly low concentrations. They consist of a hydrophilic part which loves water and a hydrophobic part which doesn't.
A lot of surfactants are strong at degreasing. This is possible because, by reducing water's surface tension, it's able to wet in around the microscopic surfaces of dirt or grime to loosen it all, helping wash it off. From here they can form a capsule around the dirt preventing it from getting back on the surface being cleaned. If you've ever wondered why your dish-washing liquid keeps grease off the plates you're washing, you now know that surfactants are behind the cause.
Another application is in the creation of hybrid oil and water based paint that lets you wash your brushes in water even though the paint is somewhat oil based. There are types of surfactant that get used as foaming agents, or even ones used to suspend anything from gases to solids in water.