Let me just quote from the README:

This is a GTK+ program to use the input devices (keyboard, mouse) of one computer as the input devices of a remote computer, via VNC. Think of it as a sort of a DIY "Synergy". The main benefit, compared to an actual VNC client, is significantly improved latency in some cases, as it never actually requests the screen contents from the remote computer.

Find it by cloning/downloading gist 2017454.