Why?
Built during a hack day, jokingly as way to provide "UUIDs as a service" in order to quickly demonstrate UUIDs and provide a way to generate UUIDs for use in code samples without a library. This service is not to be used in a serious/critical manner.
Note that ads are included with the hope that maybe it'll cover domain and hosting costs.▼ ▶ ELI5, What are UUIDs?
A universally unique identifier (UUID) is a 128-bit number used to identify information in computer systems.
We use IDs to identify "things", and usually numbers are used (e.g. #1337, #9001). It's extremely common to simply pick a number (#1) and each time a new "thing" needs an ID we'd go to the next unassigned number (#2, then #3, etc). However this can only work if we know the ID of the previous "thing", we couldn't give the ID of #5 unless we knew the previous one was #4.
In many computer systems this isn't usually desirable; either we don't get to know the ID of a "thing" we want to store (e.g. in a database) up front, or we have to do a lookup to find out what the next ID is first (inviting potential race conditions and requiring extra work).
UUIDs (Universally Unique IDs) are a popular alternative to incrementing IDs. They are designed to be generated on the fly, to be unique and to have an extremely low chance of generating a collision. When generated using sufficient entropy you're more likely to get hit by a meteorite than generate the same UUID twice.
Note that for simplification this primarily concerns UUID version 4, though rather similar there are other versions that factor in other properties such as time and network address that you can read about on Wikipedia →.