Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
Challonge - The Ultimate Source for Tournament Brackets
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
smash.gg - An esports platform empowering bottoms-up growth of competitive communities with value-add services...
Bylde - Bylde is a SaaS platform you can use to Start, Manage and Grow your groups and communities.
SportsEngine - SportsEngine is an online platform that helps users in finding youth sports programs or articles or news on different sports.