Compost toilets are a low tech, low cost, chemical free method for dealing with solid waste.
A compost toilet is waterless or dry (one that doesn't use water to take the waste elsewhere) and as a rule, they only receieve fecal deposits - that is to say, ideally, don't pee in them unless they are designed to accommodate this.
There are often two chambers; one in use, and one 'resting'. A classic compost toilet will use one chamber for a year, then change to the second chamber to allow the first to decompose for a year before emptying.
As long as there is good ventilation, such as via a vent pipe, and a drain for excess liquid, compost toilets do not smell. A handful of carbon material such as sawdust or rice straw is dropped into the toilet after use. The type of compost produced is suitable for fruit trees, trees and bushes, it is not recommended that it is used directly on the vegetable patch.