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 has already been included 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 as of 09/2016 both desktop environments will keep coexisting for the time being.
More on this topic can be found on page History of the aforementioned wiki.