What type of aircraft uses lighter-than-air gas for its lift, with no built-in means of control?

The type of aircraft that uses lighter-than-air gas for lift and does not possess built-in means of control is a balloon. Balloons rely on buoyancy created by the lighter-than-air gas, such as helium or hot air, allowing them to ascend and float in the atmosphere. The operation of a balloon is usually controlled by adjusting the temperature of the gas to gain altitude or by releasing gas to descend. Unlike other aircraft types, a balloon does not have wings or propulsion systems for maneuvering; it simply follows the wind currents for horizontal movement.

In contrast, helicopters utilize rotor blades for lift and are equipped with control systems that allow for precise navigation. Gliders are designed to soar using their aerodynamic shape, exploiting air currents for lift without an engine. Tow planes are aircraft that are designed to tow gliders into the air but do not rely on lighter-than-air gas for lift. This understanding reinforces why a balloon uniquely fits the description in the question regarding lift and control mechanisms.