Milestone Inc. (株式会社マイルストーン) is a Japanese arcade videogame developer. They are best known for shoot 'em up games developed for the Dreamcast (after the console's official discontinuation) and its arcade counterpart, the Sega NAOMI.
Milestone are made up of Japanese NAOMI arcade developers who left Compile to form their own company.
As of 2010, all of Milestone's shooters have been ported to the Wii.
Source: Wikipedia, "Milestone (Japanese developer)", available under the CC-BY-SA License.