Other vacuum tube devices

A vast array of devices were built during the 1920–1960 period using vacuum-tube techniques. Most such tubes were rendered obsolete by semiconductors; some techniques for integrating multiple devices in a single module, sharing the same glass envelope have been discussed above, such as the Loewe 3NF. Vacuum-tube electronic devices still in common use include the magnetron, klystron, photomultiplier, x-ray tube and cathode ray tube. The magnetron is the type of tube used in all microwave ovens. In spite of the advancing state of the art in power semiconductor technology, the vacuum tube still has reliability and cost advantages for high-frequency RF power generation. Photomultipliers are still the most sensitive detectors of light. Many televisions, oscilloscopes and computer monitors still use cathode ray tubes, though flat panel displays are becoming more popular as prices drop.
The fluorescent displays commonly used on VCRs and automotive dashboards are actually vacuum tubes, using phosphor-coated anodes to form the display characters, and a heated filamentary cathode as an electron source. These devices are properly called "VFDs", or Vacuum Fluorescent Displays. Because the filaments are in view, they must be operated at temperatures where the filament does not glow visibly. It is relatively easy to create highly customized VFD display designs, with all the legends required for a specific task. These devices are often found in automotive applications, where their high brightness allows reading the display in daylight.
Some tubes, like magnetrons, traveling wave tubes, carcinotrons, and klystrons, combine magnetic and electrostatic effects. These are efficient (usually narrow-band) RF producers and still find use in radar, microwave ovens and industrial heating.
Gyrotrons or vacuum masers, used to generate high power millimetre band waves, are magnetic vacuum tubes in which a small relativistic effect, due to the high voltage, is used for bunching the electrons. Free electron lasers, used to generate high power coherent light and perhaps even X rays, are highly relativistic vacuum tubes driven by high energy particle accelerators.
Particle accelerators can be considered vacuum tubes that work backward, the electric fields driving the electrons, or other charged particles. In this respect, a cathode ray tube is a particle accelerator.
A tube in which electrons move through a vacuum (or gaseous medium) within a gas-tight envelope is generically called an electron tube.
Some condenser microphone designs use built-in vacuum tube preamplifiers.

As of 2008, scores of small companies are manufacturing audiophile amplifiers and preamps that use vacuum tubes.[4]
Vacuum tube can also mean a tube with a vacuum. It is e.g. used for demonstration of, and experiments with, free-fall.

Information from Wikipedia.