The best replacement for redis is mongodb.

The best alternatives to redis are rated as following:
★★★★★  mongodb
★★★★★  memcached
★★★  cassandra
★★  couchdb
★★  riak
★★  mongo
★★  rabbitmq
★  couchbase
★  elasticsearch
★  leveldb
★  zeromq
★  varnish
★  sqlite
★  membase
★  ehcache
★  hbase
  zookeeper
  hazelcast
  mongodb performance
  berkeleydb
  appfabric
  sqs
  dynamo
  memcache
  activemq

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

Other search terms related to redis and their ratings are:
★★★★★ rails
★★★ node.js
★★★ django
★ logstash
★ persistence
★ express
magento
You have in mind a companion for redis and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of redis in all years. Click on graph for more.
redis
mongodb
memcached