Look for the terms 'wetback' and New Zealand and you'll find loads of manufacturers - names like Yunca, Woodsman, Pyroclassic, Firenzo, Osburn, Metro.
Some are water supplemental heaters, others will bring a 50 gallon tank up to boiling point and others are designed to have a few radiators attached.
Some are log burners, other pellet, and some (like mine) are multifuel (i.e. wood or coal). I run mine on the 250 trees I planted 10 years ago. 15 or so a year provide me with whole house (3200 sqft) heating for free apart from chainsaw maintenance costs a a few pints of petrol & oil.