• http://www.stackdriver.com/
• http://www.graphdat.com/
• https://www.scalyr.com/
• http://www.serverdensity.com/
• https://github.com/martinrusev/amonone
• http://word.bitly.com/post/74839060954/ten-things-to-monitor?h=2

Website/uptime monitoring:

• https://www.site24x7.com $9 for 10 monitors
• https://www.pingdom.com $11 for 10 checks
• https://www.statuscake.com, free plan with unclear limits, $25 for 50 tests
• https://uptimerobot.com, free plan 50 checks, additional 50 checks for $4.5 (decreases with scale)
• https://newrelic.com