Rockman 6 in 1 (A.K.A Rockman Super 6 in 1) is a famicom multicart that includes the first 6 mega man games in one, it is very highly regarded and a rare multicart.
One of it's noted features is that rockman 1 and 2 were converted to the MMC3 mapper that the other games use, making them compatible.
Most of the games are the exact same as their original famicom versions, except Rockman 3 gives you 30 lives (displayed as "OK" on pause screen), and Rockman 4 gives you 15 lives.
Some of the games remove any capcom copyrights, some keep them in.