Tracking changes in LaTeX with "changes" package

The changes pack­age, distributed with TeX Live, al­lows the user to man­u­ally markup changes of text, such as ad­di­tions, dele­tions, or re­place­ments. Changed text is shown in a dif­fer­ent colour; deleted text is crossed out. The pack­age al­lows def­i­ni­tion of ad­di­tional au­thors and their as­so­ci­ated colour. It also al­lows you to de­fine a markup for au­thors or an­no­ta­tions. (Here's another customised example using avatars for the author annotations.)