Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
Huntathon - Browse and submit Product Hunt Global Hackathon projects
pretix - pretix helps you to sell tickets for your event in an easy way. It supports multi-lingual events and provides a wide range of features
Foundler - Online hackathon weekends. Attend every other week.
Ticket Tribe - Sell tickets online with no fees per ticket
Confs.tech - Open source list of tech conferences: JS / Ruby / Data etc.