Wessels only joined the Toffees from Cologne last summer, but the 28-year-old has not got near the first-team due to the excellent form of number one choice Tim Howard. After only seven starts boss David Moyes deemed it was only fair to let Wessels leave in search of regular first-team football next season.
He told the Toffees' official website: "I'd like to thank Stefan Wessels who will be leaving us this summer.
"His level of professionalism has been a credit to him and he's been a great man to have around the club."
Danish midfielder Gravesen has endured a disappointing season-long loan return to Goodison Park from Celtic, making just three starts in an injury-hit campaign.
Moyes added: "Thomas Gravesen will also depart following the completion of his season-long loan. He deserves thanks for both his spells here and we wish him well for the future."