I've written a full-text search engine as well. I don't tout it as a replacement for Elasticsearch, but it does have a few advantages: it's fast; supports HTML documents; supports Polish inflection (via a full-blown morphological dictionary, not just a stemmer); and has a very compact on-disk format (pre-parsed HTML trees, Huffman-encoded over large alphabets). Oh, and it's 100% Clojure.

It underlies a concordancer GUI called Smyrna: https://github.com/nathell/smyrna, https://smyrna.danieljanus.pl

I haven't touched it in six years, other than a few small changes. But I do plan on revisiting it when time permits.