The obvious answer here is that KiwiSDR is a Software Definable Radio but what I think sets it apart from other SDRs is the ease of accessing them over the Internet with a well developed user interface that is controllable from a HTML-5 capable browser. This project started as a Kickstarter campaign in 2016. The Kiwi supports up to four simultaneous connections each with their own independently controlled audio and waterfall channels. An extension interface allows advanced signal decoding directly in the browser interface without installing additional software. Two of the popular extensions are the WSPR decoder and Time Difference of Arrival (TDoA) signal direction finder.
Many Kiwi owners have made their SDRs available to the public. In fact there are several hundred of them around the world. The easiest way to find one is pick one from a map of the world map.kiwisdr.com. If you are interested in more information about Kiwi go to their website kiwisdr.com. You can even use Kiwi to find out what your signal sounds like around the world.