The best replacement for lucene is solr.

The best alternatives to lucene are rated as following:
★★★★★  solr
★★★  sphinx
★  endeca
★  elasticsearch
★  hadoop
★  fast
★  cassandra
★  xapian
★  nutch
★  dtsearch
  compass
  hbase
  terrier
  oracle text
  swish e
  verity

Your alternative for lucene is not listed? Suggest!
Speaking about lucene, one probably shouldn't forget about nutch.

Other search terms related to lucene and their ratings are:
★★★★★ nutch
You have in mind a companion for lucene and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of lucene in all years. Click on graph for more.
lucene
solr
sphinx