Not really a thing but a major catalyst for using things. Creating smartapps/things plugins for Tasker would make for an extremely powerful combination.
So, Tasker is an automation application for android which lets you do anything. To give you an idea related to smartthings I am currently using Tasker together with Tellstick net (which I will dump as soon as I get my smartthings!). Tellstick allows me to remotely turn for example lamps and other stuff on and off through an android app called remotestick (which has plugins for Tasker).
A use case…
Tasker automatically turns wifiscan on when I am connected to the cell stations around my home,
Wifi will connect to my SSID when I am in reach of my home network.
Variable will be set @Home = 1 for example. (one can also use wifi connected to specific SSID as context)
Through a context plugin for tasker, sunset is calculated every day, in this case sunset has started which is the context besides being at home that needs to be fulfilled for the task to trigger.
Since the context at home and since we have passed sunset the action for the profile triggers and remotestick plugin in tasker sends command for my lamps to turn on. Completely automatized without me doing anything. Since I connect to my Wifi when standing outside my front door the lights are on when I enter.
Then I leave for a party and since the context at home is no longer fulfilled the exit task is triggered and the lamps are turned off.
Another simple use case is for tasker to trigger on alarm off in the morning on your phone and then starting the coffe maker. Much better than having a static time set.
So for all this to work with smartthings we need plugins for Tasker from the smartapps! http://tasker.dinglisch.net/developers.html