Loki and grafana? (not really an alternative in the sense of "full text search" over logs, but an alternative in the sense "an interface for aggregate search over logs").
Grafana started out as a fork of Kibana 3 if I remember correctly, which was around the time Elastic acquired Kibana. Since then, it has become a nice product in its own right. But the shared history is interesting.
It does look interesting, but maybe a little too exciting: "Super experimental". One advantage of loki, is that it is part of hosted grafana, so there's some commitment to it as a product.
Fluentd (https://www.fluentd.org) is a great alternative to Logstash that I've had a lot of success with. It is easy to pair with Elasticsearch and Kibana and myriad other inputs and outputs.
