Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.

Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.

Eventbrite - Discover Great Events or Create Your Own & Sell Tickets

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.

Bigtent - BigTent is a web-based organization and communication portal for groups.

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.