  Tracks and isochrones have been computed in the range of initial masses 0.15
- 20 Mo for a grid of 39 chemical compositions with the metal content Z between
0.0001 and 0.070, and helium content Y between 0.23 and 0.46. The Padova
stellar evolution code has been implemented with updated physics. New synthetic
TP-AGB models allow the extension of stellar models and isochrones until the
end of the thermal pulses along the AGB. Software tools for the bidimensional
interpolation (in Y and Z) of the tracks have been tuned. This first paper
presents tracks for low mass stars (from 0.15 to 2.5 Mo) with scaled-solar
abundances and the corresponding isochrones from very old ages down to about 1
Gyr. Tracks and isochrones are made available in tabular form for the adopted
grid of chemical compositions in the plane Z-Y. An interactive web interface
will allow users to obtain isochrones of whatever chemical composition and also
simulated stellar populations with different Y(Z) helium-to-metal enrichment
laws.
