LXQt is a lightweight Qt desktop environment.
It will not get in your way. It will not hang or slow down your system. It is focused on being a classic desktop with a modern look and feel.
LXQt is available in most Linux and BSD distributions so you may just try it out on your regular system or in a VM.
More information about installing can be found in the LXQt GitHub Wiki.
Historically, LXQt is the product of the merge between LXDE-Qt, an initial Qt flavour of LXDE, and Razor-qt, a project aiming to develop a Qt based desktop environment with similar objectives as the current LXQt.
LXQt was first supposed to become the successor of LXDE one day but both desktop environments will keep coexisting for the time being.
More on this topic can be found on page History of the aforementioned wiki.