OSG client is an interactive client package. OSG wn is a client package for batch systems.
OSG client (from VDT-Client) is practically a superset of OSG wn, it includes also:
vomses file (to make voms-proxy-init -voms... work correctly), Condor, gsiopenssh (client), PyGlobusURLCopy, PyGlobus, LCG-Infosites, LCG-Infos, scripts to request/renew certificates, Internet2 network tools (NPAD, ...), OSG Discovery.
Reference: