Introduction
First of all it is not a mod. Not a cheat or dirty hack. It is a standalone open-source application which is not interfering nor with the game, nor with the BNET app in any way. It doesn’t even reading the screen. It is plain and simple as it can be thus limited in some ways but still viable.
How it works
You set up key sequence to track on the OS level (e.g. F8 + MOUSE2) and if it has been detected the app display an icon with a timer. The skill duration for timer is also should be specified manually. Basically it can serve any other game (including D2 classic) or purpose where you can track key presses.
It won’t protect you from mistakes. It won’t preciously fire timers every single time. But still it is useful to track simple things (yes I see you stupid Werewolf hidden cooldown!).