Up until the 1980s there were plenty of small un-vented on-demand gas water heaters in several European countries (and by that I mean they could be legally bought and fitted new), even considerably longer in some countries I think. Those units were small (5 l per minute flow rate, roughly 1 1/4 GPM) and only to serve sinks. Using them to fill a bath was illegal because of the extended operating time. My dad once lived in a place with such an illegally installed one and says the fumes were definitely nasty! I think my mom wanted one fitted to the kitchen sink around 1987 and it would have been possible, except our gas pipes were too leaky for the required pressure test, even though they were still tight enough not to cause any trouble in normal use.
Cookers (kitchen stoves) were never vented in continental Europe, with very very few exceptions (I've seen ONE in my entire life). The authorities don't seem to be concerned with them either, unlike with flue-vented boilers and water heaters. If you've got one of them any extractor fans in the house must be automatically switched off as soon as the boiler kicks in!
