Chargebee - Chargebee lets you manage subscriptions and payments at scale, handle custom recurring billing scenarios, reduce subscription churn and simplify accounting.

gtop - System monitoring dashboard for terminal

Recurly - Subscription billing and recurring billing management. Recurly offers enterprise-class subscription billing for thousands of companies worldwide.

nmon - This systems administrator, tuner, benchmark tool gives you a huge amount of important performance...

Zuora - Zuora creates cloud-based software on a subscription basis that enables any company in any industry to successfully launch, manage, and transform into a subscription business.

vtop - vtop is a graphical command-line tool that uses unicode braille to chart CPU and memory usage.