While not an 'official' SEGA release, or for that matter a release that anyone wanted to properly brand, NTSC to PAL / PAL to NTSC converters were popular enough with enthusiastic gamers to include here.
You can read online for the differences between NTSC and PAL and why they exist but for the purpose of the Mega Drive, the console needed to output differently depending on the region it was used in due to the bulk of the televisions it was going to be used on conforming to either the NTSC or PAL format.
See the map below for a rough guide to the global regions using NTSC, PAL and SECAM.
The Mega Drive was also built with a regional lockout feature that prevented most games not intended for release in that specific region from running.
Converters such as the one below sat between the console and the ROM cartridge and 'tricked' the Mega Drive into allowing games that were not sold for that region to play. It also dealt with screen resolution issues that were inherent due to the nature of PAL VS NTSC displays. Some NTSC games played noticeably faster on PAL systems and a good converter would compensate for that too.
For general reference the Mega Drive can output at the following resolutions:
[PAL] 256×240, 320×240, 256×480, 320×480
|Unit pictured has been sold and its location is unknown.|