Grimsby sign Cambridge United's Nathan Arnold while Scott Brown, Craig Clay and Shaun Pearson sign new contracts.
Chesterfield turn down a bid from League Two Portsmouth for winger Gary Roberts.
Luton Town sign defender Dan Potts on a two-year deal following his release by Premier League side West Ham.
Chesterfield have turned down an offer from Portsmouth for midfielder Gary Roberts.
Relegated Cheltenham Town sign former Oldham Athletic striker Amari Morgan-Smith on a one-year deal.
Cheltenham have made their fourth summer signing with the arrival of former Oldham forward Amari Morgan-Smith.
Conference club Welling sign former AFC Wimbledon midfielder Ricky Wellard following his exit from Sutton United.
Chief executive Mark Ashton says players are attracted to League Two side Oxford because of the club's "vision" for success.