This is a very useful hiking stove you can make with a paper punch from Officeworks and some empty cat food cans. Its inception was a genius idea from Jim Woods. Be sure you only use the punch on aluminium cans. I have found that there are two sizes of aluminium can and that one fits snugly inside the other (and both inside your cup and inside your billy) so that you can have one for simply boiling and one for simmering (the one with just the single row of top holes). You may have to search delicatessens and imported food shops to find the second size now.
I have also discovered that an esbit burns so slowly in the double holed model that you can bake in your billy on top of it if you make a holey platform with legs out of aluminium flashing which fits inside your billy and suspends (eg the damper) to be cooked about an inch above the bottom of the billy.
Lots more stoves here: http://zenstoves.net/