https://nsupdate.info is a free dynamic DNS service. nsupdate.info is also the name of the software used to implement it. If you like, you can use it to host the service on your own server.
Webapp-y front-end that supports the dyndns2 protocol. Uses RFC 2136 (Dynamic DNS UPDATE protocol) to interface with DNSes that support it (BIND, PowerDNS, etc).
pwncat is a sophisticated bind and reverse shell handler with many features as well as a drop-in replacement or compatible complement to netcat, ncat or socat. Fully scriptable with Python. Self-injecting mode to deploy itself and auto-start multiple unbreakable reverse shells back to you. Reverse shells will reconnect to you if you accidentally kill pwncat or are cut off. Connections over TCP or UDP. Bind shells, reverse shells, port forwarding.
It can wrap your network traffic in any other protocol to obfuscate it or encrypt it.
Written using only with Python core libraries to allow it to run without having to install anything.
In the AUR. Also installable with pip.
This web app generates text files of netblocks in CIDR format, suitable for dropping into firewalls to deny traffic from just about any country on the planet.