I'm very glad to see this. Tyler's past grants have shown good judgment, and a level of risk tolerance unusual for a philanthropist. For people who need seed funding rather than retrospective prizes, also note that "you still can propose a coronavirus-related project through normal [Emergent Ventures] channels, with discretionary amounts to be awarded as grants per usual procedures."
Tyler Cowen's fund Emergent Ventures is offering:
Announcement: https://marginalrevolution.com/marginalrevolution/2020/03/1-million-plus-in-emergent-ventures-prizes-for-coronavirus-work.html
Side note: In the post, Tyler explains why prizes are better than grants in this situation: “The case for prizes is stronger when you don’t know who is likely to make the breakthrough, you value the final output more than the process, there is an urgency to solutions (talent development is too slow), success is relatively easy to define, and efforts and investments are likely to be undercompensated.”