Well, it would be wrong to call for Elastic Stack Competitors because Elastic Stack has been emerged as a strong competitor to many other tools in the market in recent years and is growing rapidly. Few of these are:
Open source:
Graylog: Visit https://www.graylog.org/ for more information
InfluxDB: Visit https://influxdata.com/ for more information
Others:
Logscape: Visit http://logscape.com/ for more information
Logscene: Visit http://sematext.com/logsene/ for more information
Splunk: Visit http://www.splunk.com/ for more information
Sumo Logic: Visit https://www.sumologic.com/ for more information
Kibana competitors:
Grafana: Visit http://grafana.org/ for more information
Graphite: Visit https://graphiteapp.org/ for more information
Elasticsearch competitors:
Lucene/Solr: Visit https://lucene.apache.org/ or http://lucene.apache.org/solr/ for more information
Sphinx: Visit http://sphinxsearch.com/ for more information
Most of these compare with respect to log management, while Elastic Stack is much more than that. It offers you the ability to analyze any type of data, not just logs.