YunoHost is a free and open-source self-hosting platform from France, built on Debian, offering one-click deployment of 400+ apps and built-in mail services from a single server with 2GB of RAM or more.
Sandstorm is a Y Combinator-backed (2014) open-source self-hosted web app platform from the US that isolates apps with grain sandboxes and capability security, claiming to eliminate about 95% of common vulnerabilities, though commercial maintenance ended in 2020.
Cloudron is an open-source self-hosted PaaS built on Docker and developed by Cloudron UG in Germany, with one-click app installs and auto-updates, a built-in mail server and SSO; the free plan supports 2 apps and Pro costs €15/month, ideal for individuals and teams that value data ownership.