From the website:
SearchBlox is an out-of-the-box Enterprise Search Solution built on top of Apache Lucene. It is fast to deploy, easy to manage and available for both on-premise and cloud deployment.
Best of all, it is free. No limitations. No restrictions.
Do note that downloading SearchBlox did not require registration or surrender of my phone number.
Usual questions, ease of use, ease of integration across deployments, etc.
I am gathering up a rather large data set for other purposes that I will be using to test this and other search software.