When we started Stackbit we built Unibit as an internal tool that enabled us create a theme once and convert it to multiple static site generators. When you create a new site on Stackbit using a Unibit theme you can pick any of the target SSGs for the project being generated. Unibit themes can currently be transpiled into Jekyll, Hugo & Gatsby sites.
Note: Unibit is in Beta and support is limited. We have plans to open-source Unibit but at this stage we do not have a timeline. section.