A simple mod that just counts double kills and displays them in chat. By default every double kill (1), though you can change it to any number (every 5 double kills send a message, 10, etc) by editing the line:
DoubleKillNotifier.chat_threshold = 1 <---- change to desired number.
Allow the threshold to be changed in the mod options menu in-game for ease of use (scraps of code are there but it doesn't work atm)
I kind of just made this for myself to help me track if I was actually getting them counted towards Diamonds In The Sky (Side job with the North Star for double kills)