A back door to servers.
Ingress is a Python REPL over the network to your application (very much like Twisted manhole).
Once installed, you can 'telnet <host> <port>' and run Python commands on your server environment. This is very helpful in debugging servers.
This one uses only modules found in the standard library.
Download the file for your platform. If you're not sure which to choose, learn more about installing packages.