Meson
Modern build system — faster + cleaner than CMake. Default generator: Ninja. Python-like DSL.
Jussi Pakkanen (Canonical) created 2013. Used by GNOME, systemd, GStreamer, Mesa, QEMU, Linux kernel selftests. Pitch: faster (2-5× CMake), cleaner syntax, better cross-compilation. Smaller ecosystem than CMake but rapidly growing. Competitors: CMake (more universal), Bazel (large-scale).