The Sega Dreamcast is a pretty versatile piece of hardware. Not only is it capable of running operating systems like Linux and Dreamshell et al, it is pretty adept at mimicking other console formats too. Since the early days of the Dreamcast, talented coders have been tricking the system into convincing itself it was a Nintendo Entertainment System, a Neo-Geo or even a Sony PlayStation. The latter example of console emulation on Dreamcast is well documented and eventually resulted in Bleem! being shut down by Sony's legal department, but let us also remember that Sega itself utilised the hardware of the Dreamcast to bring emulation to the masses.
While the inclusion of PC Engine and Megadrive emulators on certain Dream Passport internet browser discs is well known in the wider Dreamcast community, Sega opted to bring Genesis titles to the general populace in the United States via the Sega Smash Pack collection - an official release containing 12 retro titles from various eras in the company's illustrious history spanning both the 16 and 32-bit generations. I have it on pretty good authority that a PAL version of Smash Pack was in the works at Sega Europe (having both played a variant and by way of the article below as proof), but only the NTSC-U version ever saw the light of day.