Stack Overflow - Community-based Q&A part of the Stack Exchange platform.
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.
The Answer Bank - The Answer Bank is the UK’s leading question-and-answer site.
Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.
Askalot - Askalot is a next generation CQA (Community Question and Answer) system.
Influitive - Influitive helps companies increase customer lifetime value and accelerate sales with the power of their own customer advocates. Inspire your customers to stay longer, share their experiences, and attract new business.