Alternative to ReiserFS for storing many small files in one block?

I know that ReiserFS is able to store multiple small files in a single block, and at one time was recommended for use with s3backer because of that feature, as fewer blocks to store on S3 mean lower costs. I'm looking at using s3backer in a production system, and ReiserFS is old enough and abandoned enough that it's not a viable candidate.

Is there any "modern" Linux FS capable of doing the same sort of thing? Does EXT4 have anything similar?