Cell to Singularity uses recordings of classical music, most of which are in the public domain. Here is a list of music used in the game.
New World Symphony : Largo - Antonín Dvořák (Opening the game)
Concerto For Orchestra - Béla Bartók (game moments)
Jupiter Dance : Planets - Gustav Holst (unlocking humans)
Mars : Planets - Gustav Holst (game moments)
The Moldau - Bedřich Smetana (Civilization)
At the Terminus of the Blue : Music of the Hoh River Valley - ©2010 Prent Rodgers (Reality Engine)