Its obviously looks like a specialized screw. Maybe for teh water pipe stbs in the front yard?

looks like a pipe reamer. Its for deburring the inside of a pipe.

This is a tool designed for removing the "flexible" risers, which connect the water supply line to the sprinkler head in your yard. Despite their intended flexibility, they often break off, and this tool is used to unscrew the stub from the water supply line. You force it into the remainint portion of the riser, and turn the handle counter-clockwise - it unscrews the stub, enabling you to put in a new riser & sprinkler head.

I believe it is a pipe reamer, although it could be used to remove broken sprinkler stems. Actually now I think that is it's intended purpose - all the reamers I've seen have 5-6 blades, this looks like it has 3.

dangelo is correct. It is used for flexible risers which have broken off in an irrigation system.