Google maps. Though you might need to post a URL as an example. There's a possibility that certain sections of the site are using something different.
They don't look like the usual google maps I use and they certainly appear to have more detail about road names, stores, restaurants etc. I am quite a fan of maps (a 'cartographerophile' perhaps) and they certainly can be a godsend to remind me where I am. So thanks.
Thank you for noticing! And I agree, the map functionality the site is using is great. Fortunately @TheDude is wrong, the site is actually using Mapbox, which is much more fun for creating great maps. Mapbox adds vector layers on top of OpenStreetMap data. Sign up for an account and give it a whirl, the service allows you to do a lot for free.
For other interested forum members, try this map of Dumaguete https://www.openstreetmap.org/#map=16/9.3209/123.3026 for an example of these great maps. For me, it is almost like when b/w TV changed to colour!
But to be fair - if you are to guess then what better answer to any question than "google"? Also, when a number question I quite like the answer "4".