Every time I used WordPress in the past, I got frustrated how slow it was, even with just a few plugins. So I wrote an light-weight C/C++ core and an embeddable PHP engine to run plugins and themes, with most of the WP API surface covered.
Try the live demo, including wp-admin!
The embeddable PHP runtime that covers most of Zend PHP's features runs 2x slower than Zend, but BookPress is still faster than a performance-tuned WP instance with OPCache, page cache and object caches.
BookPress runs alongside a traditional WP installation on Linux arm64 and x86_64.
Looking forward to what you all think.