These are sometimes called counter top dishwashers. Essentially, they are less powerful and smaller dishwashers that are not fitted permanently into your kitchen. Instead they connect to your sink and sit on top of your work top. These machines are not as good as a traditional dishwasher, but they have their advantages. If your kitchen does not have any spare cupboard space to replace with a dishwasher then this may be the solution for you. These models can be very compact indeed and the smallest can be as little as 50 by 50 centimetres. This makes them ideal for very small kitchens. They are particularly geared towards smaller families or couples and they only have the capacity to wash 4-6 place settings at one time. They are also not as good when it comes to washing dishes and bans with more severe dirt to remove.
Some reviewers say that these counter top models can in fact wash dishes to the same standard as normal dishwashers. The price though, can be a deterrent. The prices are in fact no different to the standard dishwasher and you should expect to pay over £300 for a decent model made by Bosch or another reputable company. These machines go upwards of £500 like normal dishwashers, so if you have space in your kitchen they are unlikely to be the best option for you. There are other companies to consider here as well such as Indesit, so it might be worth going outside the normal brands if you think this option is for you. There are much fewer table top dishwashers on the market in general so it is quite possible to assess all the options in a relatively short time. Some companies like dishwashingexpert.co.uk offer a service to help you compare different types of dishwasher as well as different brands and individual models.