Zabbix - Track, record, alert and visualize performance and availability of IT resources
Do You Even List? - Auto updating Twitter list of people you interact with most
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.
Listr - Listr lets you explore some of the best lists on Twitter, curated across your favorite categories.
Prometheus - An open-source systems monitoring and alerting toolkit.
Vicariously.io - Create Twitter lists based on the follows of other users