New flat-file based CMS - no database required. Benefits simply equate to speed, and a responsive control panel. Does require writable server-side files however, but this could be negated by pairing with something like GIT. $19-$99. Nice.
Speaking from painful experience, sometimes going backwards is the best way to move forwards. Removing the overhead of modern CMS systems for flat-files is the biggest performance gain you'll ever get.
Inevitable that I post this, having managed 200+ sites with it over the years. Concrete5 simply outclasses the other main players. Move you (or your client) from WordPress to C5, & the veil will be lifted. Easy to use, & getting better with every release