Capcom bundled all four Mega Man Zero games in a single release for the Nintendo DS titled Mega Man Zero Collection (Rockman Zero Collection in Japan). The game was released in North America on June 8, 2010, two days later in Japan and Australia, and was slated for release in Europe on 11 June 2010, however, release in the European region has been patchy, with the game not being released in some nations.
No changes have been made to the games in comparison with the original versions, but a few new features were added to the compilation, like an artwork gallery and the ability to remap certain actions to different buttons, as well as an "Easy Scenario" mode that allow the four games to be played as if they were as a single one, with some alterations to make the game easier (e.g. blocks covering spikes, no need to feed Elves, etc.).
Source: Wikipedia, "Mega Man Zero Collection," available under the CC-BY-SA License.' '