I believe Tobiasz is referring to activity of tapping a tempo, i.e. setting a certain unit of time to the interval between two taps. It's an intuitive way to set the tempo (BPM) and very useful in live performances. For example, the delay of Line6's Echo Park can be set by double-tapping. 

As far as I know (which may not be adequate ;]), there is no such feature yet.

2011/7/31 Aniol Marín <loquetudigas_loquetudigas@hotmail.com>
do you mean something like a metronome? I always make a basic drum rhythm for that.

From: unfa00@gmail.com
Date: Fri, 29 Jul 2011 12:22:54 +0200
To: LMMS-devel@lists.sourceforge.net
Subject: [LMMS-devel] Tap tempo.

Hello! is it possible to tap tempo in LMMS?

Tobiasz unfa