Programs that come equipped with alarms to notify you at a certain time there are many, most of them full of functions, tools and even text editors to write reminder notes about the messages of each alarm. But if what you are looking for is quite the opposite, then what you need is Alarm Clock.
Alarm Clock is, above all, simplicity personified, because you simply have to indicate with four figures the time you want to be notified (for example, 1730 for 5.30 in the afternoon) and will notify you at that time. The alarm sound is the same as the standard Windows sound at startup. Of course, Alarm Clock is completely free and does not even require installation.
For programmers it is of interest that on the website of the author of Alarm Clock they have the source code (in C), which will allow them to know how this program has been carried out.
You can free download Alarm Clock 32, 64 bit and safe install the latest trial or new full version for Windows 10 from the official site.