There was a recent HN Post for codequestion which builds an offline semantic index (using https://github.com/neuml/txtai) on the archive.org Stack Overflow dumps - https://news.ycombinator.com/item?id=33110219

GitHub: https://github.com/neuml/codequestion

Article: https://medium.com/neuml/find-answers-with-codequestion-2-0-...