VOGSY - Professional service automation tool built on Google G Suite

Todo.txt - Track your tasks and projects in a plain text file, todo.txt. A todo.

HarmonyPSA - HarmonyPSA - Professional Services Automation (PSA) for IT Businesses

Task Coach - Task Coach is a simple open source todo manager to keep track of personal tasks and todo lists.

Timewatch - Timewatch offers time tracking, expense management, resource scheduling and professional services automation solutions.

Strikethru - Strikethru is a kind of to-do list notebook for managing work lists and staying updated with the important tasks.