Q4OS is a Debian-family Linux distribution based on Debian Stable. Blazing fast, ultra-stable desktop featuring the Trinity Desktop Environment (KDE 3.5 revival).
Strengths: Can install straight from Windows with a setup.exe wizard; Trinity Desktop uses under 300MB RAM with high responsiveness; Rock-solid Debian stable foundation. Trade-offs: Classic Windows 2000/XP style interface looks dated to modern users.