Giftbit Payment API - Stripe for gift cards
Zabbix - Track, record, alert and visualize performance and availability of IT resources
Felt for iPhone - Handwritten cards for the modern world
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.
Raise - The easiest way to save money on the go
Prometheus - An open-source systems monitoring and alerting toolkit.