This is a VERY useful hiking stove you can make with a paper punch from Officeworks and some empty cat food cans. I have found that there are two sizes 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).
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.
A windscreen of the same material (flashing) is also a good idea (and also fits inside your billy): http://jwbasecamp.com/Articles/SuperCat/
Lots more stoves here: http://zenstoves.net/