Well, that's hard. Standardizing evaluation (critical to reducing bias) requires that everyone (or a lot of people) see a similar problem. And when someone is working on their own time, I think it's important that there's not working code easily accessible online. Perhaps this can be overcome by asking candidates to talk through their code after they are done

In most of the work at home projects I've been given there was a ton of available code online, they've primarily been for front-end positions so it's usually "Make a small app using your favorite library"

I can't imagine there are that many 3-4 hour projects that won't already have available code. The most important part of an at home project in my opinion is the walk through.

The best interview I had asked me to go through the project and explain the what and why I did things and asked for high level understanding of what the framework I chose or the browser/node was doing based on what I wrote.

It was an app in React and they went through why I decided to make a component for x, y but not z and then asked if I understood the virtual DOM as a concept.

To me that's the best you can do, you need to understand how the programmer thinks about problems, works through them and that they are engaged in the ecosystem at large.

if you change the assessment every so often, you could permit people to release their work eventually.

If someone solved a significant problem at your request, but despite this you did not hire them or otherwise compensate them for that work, I don't see how you have any right either legally or ethically to expect them not to then use the work to advertise what they can do to anyone else. The premise is one-sided enough already (though the argument elsewhere in this HN discussion that it might be preferred by nervous interviewees is an interesting one I haven't noticed before) and I think expecting any sort of loyalty or confidentiality after the process has ended is rather optimistic.

I like that idea!

I am curious why you have that requirement. What is the fairness you are striving for?

If I invest time to do something, it better be worth it for me.

Like getting a job?

A lot of companies will ask for existing code examples, in this way I can just point them to my example-code github repo and I've had companies use that instead of asking me to do a specific challenge for them.