In my system it is called "librecad". I guess qcad is non-free somehow.
The biggest difference I see between these two is UI and the pace of development. LibreCAD is still being worked on, but the latest stable release was in 2016. Last patch for QCAD has been released four days ago.
Personally, I prefer QCAD to LibreCAD. Both are quirky to use, but QCAD is at least a little bit less quirky. If you are coming from AutoCAD, then both will be equally confusing.
[0] Maybe not literally, README file available in LibreCAD repo declares that "LibreCAD is a 2D CAD drawing tool based on the community edition of QCAD." On the other hand, Libre Arts article [1] calls it fork.
LibreCAD in same time has a better performance with big/complex drawings, than QCAD.
LibreCAD has not-great DWG support and is free. Last I remember reading about it, they were looking to get better DWG support via the LibreDWG library, but they needed to strip out and fully rewrite a bunch of old QCAD code to achieve that, due to licensing issues.