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Jekyll is a highly popular SSG. It is well documented, and supports quite a lot of features out of the box. It does have some specific structure specifics enforced on the project and content however. It also seems quite a large project with much documentation which can be a catch 22 for this problem at the start, but may be something to look at once we have some initial SSG in place. Jekyll doesn't seem to support HTML files as content or if it does, it is a plugin which was not easily located, and expects a Markdown file.
Metalsmith (Node JS)
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