  We present a dense grid of evolutionary tracks and isochrones of rotating
massive main-sequence stars. We provide three grids with different initial
compositions tailored to compare with early OB stars in the Small and Large
Magellanic Clouds and in the Galaxy. Each grid covers masses ranging from 5 to
60 Msun and initial rotation rates between 0 and about 600 km/s. To calibrate
our models we used the results of the VLT-FLAMES Survey of Massive Stars. We
determine the amount of convective overshooting by using the observed drop in
rotation rates for stars with surface gravities log g < 3.2 to determine the
width of the main sequence. We calibrate the efficiency of rotationally induced
mixing using the nitrogen abundance determinations for B stars in the Large
Magellanic cloud. We describe and provide evolutionary tracks and the evolution
of the central and surface abundances. In particular, we discuss the occurrence
of quasi-chemically homogeneous evolution, i.e. the severe effects of efficient
mixing of the stellar interior found for the most massive fast rotators. We
provide a detailed set of isochrones for rotating stars. Rotation as an initial
parameter leads to a degeneracy between the age and the mass of massive main
sequence stars if determined from its observed location in the
Hertzsprung-Russell diagram. We show that the consideration of surface
abundances can resolve this degeneracy.
