What is the major difference between Redis and Membase?

I'm adding some points to Manto's answer:

1. Redis has built in transaction mechanism, while membase does not. Base on your work it may be critical
2. Master-master replication have some cons compare to master-slave: loosy consistent (lazy object, async...), more complex compare to master-slave (hence add some latency).
3. Current version of redis (2.x) does not support clustering. You'll need to shard the database manually (check http://antirez.com/post/redis-presharding.html), while membase support clustering out of the box and have a pretty nice monitoring gui.
4. (Benchmark may be ** but people just love dirty things) Redis seems to have slight performance edge at heavily concurrent case. (http://coder.cl/2011/06/concurrency-in-redis-and-memcache/)