Not a clone, I've been developing a blogging platform with the same basic feature sets called CiiMS [1] since 2011, which is written in PHP. Unlike Ghost however, CiiMS has a working API, comprehensive documentation [2], and a dashboard. We also offer our own hosting as well [3].

[1] https://github.com/charlesportwoodii/ciims [2] https://docs.ciims.io [3] https://www.ciims.io