Slax

Slax is a compact, fast, and modern Linux operating system that combines sleek design with modular approach. With the ability to run directly from a USB flash drive without the need for installation, Slax is truly portable and fits easily in your pocket.

Super lightweight and resource efficient, It makes a good alternative to Lubuntu for older, low spec hardware and unlike Lubuntu it still supports 32-bit systems as well as modern 64-bit systems.