Courtesy of stephendedman (thanks!) comes this video of a hybrid recumbent/upright that can switch modes midride.
The idea is to have a recumbent where you can switch to a standing position for hill climbing (so that you can use your body weight). I'm not sure the advantage is worth the weight penalties* or the risk to the knees from mashing. I can't mash so I've learnt to watch my cadence and keep spinning at 80-100 which is a lot better for the knees.
*There are at least two: the extra parts for the concertina mechanisms and the fact that the handlebars have to be load bearing in the upright position.