Heka by Mozilla is another alternative - http://hekad.readthedocs.org/en/latest/. I have been running in production to ship docker logs to our Elasticsearch cluster.
Heka's really nice, and the lua sandbox makes it easy to write new codecs.
We (OVH) recently tried Heka to push syslog data into Kafka, but it eventually kept crashing under load.
Other alternatives were way to slow for our needs.