Every Linux Networking Tool I know...
ping - are these computers even connected?
curl - make any HTTP request you want
httpie - cURL-like tool for humans
wget - downloading files
tc - show / manipulate traiffc control settings
dig/nslookup - what is the IP address for that domain?
whois - check domain registration
ssh - secure shell
scp - file copy over a ssh connection
rsync - copy only changed files (works over SSH)
ngrep - grep for network
tcpdump - dump traffic on a network
wireshark - dump traffic on a network with a GUI
tshark - dump and analyze network traffic
tcpflow - TCP flow recorder
ifconfig - what is my IP address
route - view / change routing table
ip - replaces ifconfig, route and more!!
arp - ARP table
mitmproxy - spy on SSL connections your program are making
nmap - Port scanning
zenmap - nmap with GUI
p0f - identify remote systems passively
openvpn - VPN
wireguard - VPN
nc - netcat! make TCP connections manually
socat - proxy a TCP socket to a unix domain socket
telnet - like ssh but insecure
ftp/sftp - copy files. sftp does it over ssh
netstat / ss / lsof / fuser - what ports are server using?
iptables - setup firewalls and NAT
nftables - new version of iptables
hping3 - construct any TCP packet you want
traceroute / mtr - what servers are on the way to that server
tcptraceroute - use TCP packets instead of ICMP to traceroute
ethtool - manage physical Ethernet connections + network cards
iw / iwconfig - manage wireless network settings (see speed/frequency)
sysctl - configure Linux kernel´s network stack
openssl - do literally anything with SSL certificates
stunnel - make a SSL proxy for an insecure server
iptraf / nethogs / iftop / ntop - see what is using bandwith
ab / nload / iperf - benchmarking tools
python -m SimpleHTTPServer Port - server files from a directory
ipcalc - IPv4 netmask/broadcast/etc calculator
nsenter - run program in different namespaces