I’d quit my job, buy a small house for my partner and I and give enough to my family that they wouldn’t have to worry about money again.

With the rest, I’d set up a trust that donates 1% per year in microgrants to free software maintainers who apply to it. Similar to NLnet, but with no strings attached beyond continuing to maintain the project.

Then, with all my free time, I’d also work on free software.