How do I integrate MongoDB with Solr?
I haven't done any integration, and I'm sure you've already googled, but...
http://nosql.mypopescu.com/post/383437318/integrating-mongodb-with-solr
http://blog.knuthaugen.no/2010/04/cooking-with-mongodb-and-solr.html
The issue you are probably going to run into with a "psuedo real-time" solution, depending on your volume, is performance. Solr performance with high commits isn't the greatest. In other words, its not really so much of a real-time indexing solution as it is a batch indexing solution. Depending on what you're actually doing this may or may not be an issue for you.
ElasticSearch (mentioned above) has been making a lot of noise in the blogosphere lately and it has a JSON api, so you might want to look at it if you're using MongoDB. I've run across these performance metrics when doing some research on real-time commits (I've never used ElasticSearch, though).
AFAIK, there is only one (highly dedicated) contributor to ElasticSearch.