The Touhou Project is a series of 2D vertically-scrolling danmaku shooting games developed by Team Shanghai Alice, whose only member is a Japanese game maker who goes by the pseudonym of ZUN. They are similar to other shooting games, however, they focus more on working your way through complex bullet patterns containing anywhere from 10 to 100 bullets. These many complex bullet patterns are what make the series popular, as well as the large focus on characters and well-developed storylines it contains.
PC-98 predecessor games
The Touhou series first began on the PC-98 series of computers, the development team at the time being Amusement Makers, with the first five games being native to that platform. Considering the PC-98 series was already on the decline well before the series began, the first five games are not very well known amongst players.
After four years of inactivity, the creator of the series, ZUN, left Amusement Makers and went on to found Team Shangai Alice. He began developing the rest of the series for Windows, which substantially improved their playability, graphics and sound when compared to the PC-98 games.
In addition to the ZUN developed shooters, a number of official spin-off 2D fighting games were developed in cooperation with Twilight Frontier. While technically 2D fighters, they take strong influences from the bullet hell action of the main games with the majority of attacks producing projectiles and the latter games even moving the action to mid-air.