Nobody has. There's no visibility or community around it which is a constant problem with Yahoo's open source projects. The only thing that really took off was Hadoop but there was very little back then.

Vespa is also far more heavy and complex than any other search systems mentioned here.

Can you tell us why you like it?

Has been in production far longer than any other open source solution. Runs at scale across Yahoo, powering even Ad systems, with live configurations pushes. Everything you need for highly available product. It also has capabilities to be used for more complex uses cases around AI.