OpenMandriva Lx is a cutting edge distribution compiled with LLVM/clang, combined with the high level of optimisation used for both code and linking (by enabling LTO, and profile guided optimizations for some key packages where reliable profile data is easy to generate) used in its building.

OMLx 4.0 brings a number of major changes since 3.x release:

Immediately visible to everyone:

KDE Plasma has been updated to 5.15.5 (with Frameworks 5.58 and Applications 19.04.2, Qt 5.12.3);
LibreOffice is now working with complete Plasma integration, giving the user familiar system dialogs and an improved look and feel;
Falkon, a KDE web browser that uses the same rendering engine as Chromium, is now the default browser, reducing the memory footprint and delivering a more consistent UI;
Since the problematic patents on MP3 have expired between the Lx 3 and 4 releases, MP3 decoders and encoders are now included in the main distribution. Video and Audio players have also been updated.
OpenMandriva brand-name applications:
OM Welcome has been updated a lot and OM Control Center is now included in the main distribution;
OM Control Center replaces the dated DrakX tools;
OM Repository Management Tool (om-repo-picker), a frontend for DNF package repository selection, is now available
Live mode:
ISO menu new entries for language and keyboard preference
Upon user’s request, KPatience card games have been included in ISO (live mode only)
Calamares new features:
Easy swap partition option
Calamares log copied to successfully installed system
Automagically removing all unused languages at the end of installation
Calamares now checks whether system is installed in VirtualBox or in real hardware. If in real hardware it removes virtualbox unuseful packages.
Lots of changes are not immediately visible to end users but very important for developers maintaining the system, enabling us to improve the system even faster in the future. Among them:

Switch RPM to version 4 and to DNF as software package manager;
The toolchains have seen a number of changes. The main C/C++ toolchain is now built around clang 8.0, glibc 2.29 and binutils 2.32, with new wrappers that make it possible for tools like nm to work with LTO files generated by either gcc or clang. gcc 9.1 is also available;
The Java stack has been updated to use OpenJDK 12 with package dependencies built around Java Modules.
Python has been updated to 3.7.3, and we have successfully removed dependencies on Python 2.x from the main install image (for now, Python 2 continues to be available in the repositories for people who need legacy applications);
Perl, Rust and Go have also been updated to current versions;
All important libraries have been updated to current versions (e.g. Boost 1.70, poppler 0.76);
The kernel has been updated to version 5.1.9 with additional performance improvements. Kernel 5.2-rc4 is also available in the repositories for testing.