Lubuntu is described as 'Fast and lightweight operating system with a clean and easy-to-use user interface. It is a Linux system, that uses the minimal desktop LXDE/LXQT' and is a very popular Linux Distro in the os & utilities category. There are more than 100 alternatives to Lubuntu for a variety of platforms, including Linux, Self-Hosted, Windows, Mac and Raspberry Pi apps. The best Lubuntu alternative is Linux Mint, which is both free and Open Source. Other great apps like Lubuntu are Ubuntu, Fedora, Zorin OS and elementary OS.
With the XFCE desktop, Mint isn't quite as lightweight as Lubuntu, but it is still fast and a good choice for older hardware.