From Sega Retro
The PC Engine (Japan)/TurboGrafx-16 (US) (it was never officially released in PAL regions, though did see some sales as the TurboGrafx in the United Kingdom and France) was a home console developed by NEC and Hudson Soft in a collaborative effort between 1987 and 1994 (Japan)/1989 and 1995 (US). The system combined a Hudson-produced 8-bit CPU, the HuC6280A (an enhanced 6502 — the TurboGrafx-16 was, in fact, 8-bit — with a six-channel PCM sound system with a few perks) and rather capable video hardware (variable screen resolution, many colors on screen at once and very large sprites, though only two sprite "layers" with a background layer in between). Games were distributed on "HuCards" — effectively a ROM board on a card. There was also a CD add-on which also saw some Sega releases.
While Sega initially supported the platform to some extent, the Sega Mega Drive entered the market in direct competition and so Sega focused their efforts on their own console. In the US, the TurboGrafx-16's marketing was poor (only being sold in major cities and with little advertising), and hence the console landed in a distant third after the Mega Drive and Super Nintendo, but in Japan the tables were turned, with the PC Engine greatly outselling the Mega Drive. This prompted Sega to back the console until the release of the Sega Saturn.
With the exceptions of Fantasy Zone and Space Harrier, all these games were PC Engine exclusives (not released in the US).