The following is a very quick summary. See the Crippling Wave rune effects page for a more thorough description of rune effects, or any of the individual rune pages for numbers, screenshots, blue quotes, and much more.
During the beta, all the skills previously known as combos were simplified down so much that only three of them (Fists of Thunder, Deadly Reach, and Crippling Wave) still contain any semblance of combo functionality. These three skills now provide simply an additional effect on every third strike, while the others (Way of the Hundred Fists, Exploding Palm, and Sweeping Wind) now have a single function on every strike. Combos previously consisted of: the normal spell attack on the first strike; a stronger attack on the second; and on the third, an even stronger attack coupled with an additional effect.
Crippling Wave was first shown at BlizzCon 2009 as one of the original skills when the Monk was unveiled. Flux was able to try it out:
This one seems like it would be very useful against big bosses, since it makes them susceptible to damage, while making them deal less to you. Throwing in stage 2 or 3 of this in the midst of other more useful combo attacks could be helpful, now and then, since the curse-like debuff can hit multiple enemies in close proximity.
Crippling Wave was still in the game at BlizzCon 2010, but there are no gameplay reports from that event discussing this skill.
The beta started in September 2011, and Crippling Wave became a level 8 skill. The skill system was once again overhauled for the Beta Patch 13 in February 2012, and Crippling Wave was classified as a Techniques skill and moved to level 14. For Beta Patch 14, it was re-classified as a Primary skill, moved to level 11, and buffed a bit.