Graylog is an open source syslog implementation that stores your logs in Elasticsearch. It consists of a server and web interface written in Java that accepts your syslog messages via TCP or UDP (or GELF messages) and stores it in the database.
Datadog is a monitoring service for IT, Dev & Ops teams who write and run applications at scale, and want to turn the massive amounts of data produced by their apps, tools and services into a unified view of IT infrastructure. 120+ Integrations!.
Mac-OSX Syslog Center is syslog server monitor and analyzer software for syslog events and notifications that supports any vendor and helps to monitor, analyze, report and correlate real-time network events.