Redis - Redis is an open source in-memory data structure project implementing a distributed, in-memory key-value database with optional durability.
Fluentd - Fluentd is a cross platform open source data collection solution originally developed at Treasure Data.
memcached - High-performance, distributed memory object caching system
Datadog - See metrics from all of your apps, tools & services in one place with Datadog's cloud monitoring as a service solution. Try it for free.
MongoDB - MongoDB (from "humongous") is a scalable, high-performance NoSQL database.
Splunk - Splunk's operational intelligence platform helps unearth intelligent insights from machine data.