If you mean running the Solr server on .Net instead of Java, then no, there is no port. I’ve been trying to run it with IKVM here but it’s low-priority to me so I can’t put much time on it. It’d be great if someone can help out with this.
If you mean using/connecting to Solr from a .Net application, then yes, you can use SolrNet or SolrSharp for that.
I blogged about this not long ago.
UPDATE: I made significant progress with Solr + IKVM.