I'm unclear about the requirements for using Couchbase-lite.
Is it possible to use Couchbase-lite with CouchDB? Or does Couchbase-lite require Couchbase Server and Sync Gateway? Thanks!

According to the documents it is 100% compatible with both CouchDB and Couchbase.

~~http://docs.couchbase.com/couchbase-lite/cbl-concepts/#can-couchbase-lite-replicate-with-apache-couchdb-servers~~

Also I found this blog post on syncing IOS with CouchDB, might be useful! http://blog.lunarlogic.io/2013/synchronization-using-couchdb/

Edit

Official Couchbase link above isn't valid anymore however the following official article from Couchbase lists the other databases that are compatible: (CouchDB,PouchDB,Cloudant)http://developer.couchbase.com/documentation/mobile/current/develop/guides/couchbase-lite/native-api/replication/index.html

Couchbase Lite implements the CouchDB replication protocol and is 100% compatible with CouchDB. However, Couchbase Server does not require certain document metadata that CouchDB documents contain for performance reasons. Sync Gateway is how the necessary meta-data gets added to Couchbase Server.

As of Couchbase Lite 2.0, it is no longer compatible with CouchDB. It now requires a Sync Gateway. You will need to use Couchbase Lite 1.x.

The new protocol is incompatible with CouchDB-based databases. And since Couchbase Lite 2 only supports the new protocol, you will need to run a version of Sync Gateway that supports it.

https://docs.couchbase.com/couchbase-lite/2.1/swift.html#compatibility

I just started using recently using but I hope My answer will be use for some scenario..

coming to your question It all depends on your requirement..