The former Newcastle striker, now 34, departed after making the 50th appearance for Kettering.
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Ranger was joint-second top scorer in the seventh-tier Southern League Premier Central this season with six goals in 10 games, and had 18 goals in all competitions.
"His commitment to the club, both on and off the pitch, is a testament to him," club owner George Akhtar told the club's website.
"You will be missed. Big players step up in big games and that's what epitomises Nile Ranger."