Linux enumeration
LinEnum
LinEnum is a basic shell script that performs over 65 checks, getting anything from kernel information to locating possible escalation points such as potentially useful SUID/GUID files and Sudo/rhost mis-configurations and more.
enum4linux
enum4linux is a wrapper around the Samba tools smbclient, rpclient, net and nmblookup.
netcat
netcat is network debugging and investigation tool that can assist with port scanning, transferring files, and port listening, and it can also be used as a backdoor. Many descendants.