Lubuntu

Lubuntu started life as a distro designed to run on older, slower, and lower-spec hardware, and that remains one of its selling points: It needs as little as 1GB of memory (though, like Kubuntu, there are no official minimums).

But its developers have fine-tuned its approach in the past couple of releases, focusing on a light but more modern distro. Hence the move to the LXQt desktop, the Calamares installer used by Fedora, the KDE Muon software center, and the decision to drop the 32-bit version.