Beats - Single-purpose data shippers that send data from hundreds or thousands of machines and systems to Logstash or Elasticsearch. (Source Code) Apache-2.0Go
RRDtool - Industry standard, high performance data logging and graphing system for time series data. (Source Code) GPL-2.0C
Statsd - Daemon that listens for statistics like counters and timers, sent over UDP or TCP, and sends aggregates to one or more pluggable backend services. MITNodejs
tcollector - Gathers data from local collectors and pushes the data to OpenTSDB. (Source Code) LGPL-3.0/GPL-3.0Python
Telegraf - Plugin-driven server agent for collecting, processing, aggregating, and writing metrics. MITGo