InfluxDB is an open source time series database with no external
dependencies.  It's useful for recording metrics, events, and performing
analytics.

Features:

 * Built-in HTTP API so you don't have to write any server side code to
   get up and running.
 * Data can be tagged, allowing very flexible querying.
 * SQL-like query language.
 * Simple to install and manage, and fast to get data in and out.
 * It aims to answer queries in real-time. That means every data point
   is indexed as it comes in and is immediately available in queries
   that should return in < 100ms.

Homepage:
https://github.com/influxdata/influxdb
