diff --git a/open_muscat-xapian.md b/open_muscat-xapian.md
new file mode 100644
index 0000000..c14374b
--- /dev/null
+++ b/open_muscat-xapian.md
@@ -0,0 +1,7 @@
+
+The [Xapian][10] information retrieval library was forked circa 2001 from the last
+version of [Open Muscat][20] released under the GPL.
+
+[10]: https://en.wikipedia.org/wiki/Xapian
+[20]: https://xapian.org/history
+