A computer game genre almost as popular as worm games or Tetris (ie. every programmer had to make one) during the 1990s, especially in Finland. The idea of cave flyers is that each player (all of them had split-screen multiplayer) controls a small ship in a cave-like level (like the genre name implies), trying to shoot other players' ships with a small pea gun and a variety of special weapons. One could argue on what game actually started this genre, and whether games like Lunar Lander belong to the genre, but Turboraketti is widely accepted as the first and certainly the most legendary cave flyer. At least it started the Finnish cave flyer boom, although eg. the much earlier games Thrust and Omega Race could be considered to belong to the genre.
All of the cave flyers were very similar to each other, mostly differing only by their special weapons (and even they were usually almost the same) and small nuances in play mechanics. Even the ships in almost all of them looked the same, V-shaped (probably attributable to programmer-drawn graphics). Yes, some of them had different ships you could choose from, nice graphics or some catchy (but worthless) feature like flowing water or the ability to eject from your ship and walk around the level as a soldier. The truth is, most of them were very amateurish and had very unbalanced play mechanics, resulting in for example only a few of the special weapons being usable. A few good quality exceptions from my own experience based on addictiveness: A-Wing, AUTS, Gravity Force and Rocket Chase.
Here are some of the better known cave flyers, in alphabetical order. A-Wing, AUTS, A2, Gravity Force, KOPS, Rocket Chase, Tappo II, Turboraketti, V-Wing, Wings (You can /msg me if you know others I should add to the list).