I use Middleman almost exclusively. It gives me almost the simplicity of Jekyll but with all the flexibility of writing and including Ruby whenever I feel like it (which can be bad...). I've written things that are almost akin to a small read-only Rails app except the data is stored as YAML files.
If I had to move from Ruby, I think I'd give Lektor (made by the creator of the Python Flask web framework) a deep look. Besides being a static site framework, its creator has endeavored to build a client-friendly GUI, making it a potential way to build static sites that can be maintained by laypersons. It has a very opinionated structure, which had caused me to rethink how I arrange files in my other static projects: https://www.getlektor.com/