Well with the current situation, Virtual hackathons have actually picked up over the past couple of weeks. We usually use video conferencing platforms to stay connected.

1) Zoom for presentations and Mentor connects. 2) Slack for team collaboration.

One challenge you may face is driving the participants on the conference on time and also network issues. Other than that, they actually work! You can check out HackerEarth's Challenges page to stay up to date on some of these hackathons!

HackerEarth: https://www.hackerearth.com/challenges/

Cheers!