Version 1.2.0 arrived at a turning point:

Troubleshooting and Legacy Guide: Mono for Android v1.2.0.24718.zip

This version refined the plugin for Visual Studio 2010, allowing Windows developers to stay within their favorite IDE while deploying to Android emulators and physical devices.

Mono for Android v1.2.0.24718.zip contains the installation packages for an early version of the Mono for Android (now known as Xamarin.Android

Released in late 2011, version 1.2 was a foundational update for the platform before it was rebranded to Xamarin. It allowed .NET developers to build native Android applications using C# and the Mono Project Mono Project Key Technical Features

Install a legacy operating system (like Windows 7) inside a virtual machine (e.g., VirtualBox or VMware) with no internet access. Extract and run the zip file only within this environment.

So if you’re unpacking that old ZIP file, you’re looking at a direct ancestor of Microsoft’s modern, unified mobile and desktop framework.