Audacity is an open source audio editing software which works on almost all operating systems including Linux, Mac, windows etc.
*Can record from microphones or any other source, there is no time limit.
*Simple to edit interface, thus it easy to combine or split audio files.
*Job gets performed at a quick pace.
*Alters the pitch without altering the tempo, or vice-versa.
*Remove static, hiss, hum, or other constant background noises.