Impacket is a Python library and collection of tools for Windows protocol interaction — secretsdump.py (credential dumping), psexec.py/wmiexec.py (remote execution), GetNPUsers.py (AS-REP roasting), GetUserSPNs.py (Kerberoasting).
Impacket is essential for Windows/AD pen testing. GetUserSPNs.py -request: Kerberoasting. GetNPUsers.py: AS-REP roasting. secretsdump.py via DCSync or local NTDS: credential extraction. smbclient.py: enumerate SMB shares. All run from Linux against Windows targets.