Jama - Jama combines requirement management software with enterprise collaboration capabilities to solve product delivery problems.
Trello - Infinitely flexible. Incredibly easy to use. Great mobile apps. It's free. Trello keeps track of everything, from the big picture to the minute details.
Reqtify - Reqtify is an easy to use, interactive application for managing requirements.
Notion - All-in-one workspace. One tool for your whole team. Write, plan, and get organized.
ReqView - Simple and powerful requirements management tool enabling easy requirements gathering, traceability tracking and offline collaboration.
Slack - A messaging app for teams who see through the Earth!