Comment by nostrademons

Google Maps as it launched was the integration of 3 pre-existing products: KeyHole (John Hanke, provided the satellite imagery), Where 2 (Lars & Jens Rasmussen, was a desktop-based mapping system), and Google Local (internal, PM was Bret Taylor, provided the local business data). Note that both KeyHole and Where 2 were C++ desktop apps; it was rewritten as browser-based Javascript internally. Soon after launch they integrated functionality from ZipDash (traffic data) and Waze (roadside events).

People read that YouTube or Android were acquisitions and don't realize just how much development happened internally, though. Android was a 6-person startup; basically all the code was written post-acquisition. YouTube was a pure-Python application at time of acquisition; they rewrote everything on the Google stack soon afterwards, and that was necessary for it to scale. They were also facing a company-ending lawsuit from Viacom that they needed Google's legal team to fight; the settlement to it hinged on ContentID, which was developed in-house at Google.