A: Likely a play on "Microsoft," designed to appear official or to game search engine algorithms. "Mu" is also a Greek letter used in hacking subcultures.
A: GOG.com for classic PC games; Internet Archive for abandonware; RetroArch for emulation. mu soft game pack link
Today, you have superior options: legal classics for pennies, safe emulation, and community-supported abandonware archives. The price of "free" via a shady link is simply too high. A: Likely a play on "Microsoft," designed to