This is a nice little rapidfire hack I found a few days back. This is NOT a client and only requires you to have .net framework 3.5 or higher. This rapidfire hack will work for all versions of minecraft.
This rapidfire hack worked on almost every server that I tried, sometimes nocheat would throw a fit so please use it with care.
Hotkeys: Hold “R” to start the rapid fire
Insert = Hide/show
Delete = close