Foundler - Online hackathon weekends. Attend every other week.
Founders Nation - Find or become a startup cofounder
CoFoundersLab - Meet 250,000+ entrepreneurs online
HackHub - Host tech events and hackathons with ease 👨💻🛠
CollabFinder - Find cofounders and makers to help build your project
Confs.tech - Open source list of tech conferences: JS / Ruby / Data etc.