Apple Events for macOS - The unofficial Apple Events app for macOS
Meetup - Helps groups of people with shared interests plan events and facilitates off line group meetings in various localities around the world.
TechEvents.co - Tech and startup events aggregator
Event Hunt - Startups and Tech Events Curated By Locals
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Mobilizon - A free and federated tool to get our events off Facebook