LibreCAD is a fork [0] of QCAD Community Edition. It looks very similar, but it is actually a separate piece of software.
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.