Ask HN: How do you build your freelance work portfolio of closed source apps?

99% of the software I've written has been embedded deep inside some expensive piece of machinery. A visual portfolio would be useless since it would consist of photos of the machine, which would offer no insight. Instead I describe what I've done, how it works, problems I had to overcome, etc.

I've interviewed people for many types of positions, and I can't think of a single time when the ability to answer questions about the software they've written wouldn't have sufficed. As it is, I rarely even get that :-(

Instead, focus on other ways to show what you've done and - more importantly - what you know. Blog posts are easy but it's unlikely prospective clients will dig through blog archives to find a problem relevant to them. Instead, you could likely discuss an application in vivid technical detail without mentioning the client and not be breaking any NDA or contract rules. Think of it as a white paper to host on your site as something a little more in-depth than a blog post.

I created a personal website to which I would grant limited access to select portions and only to those potential employers for which I was actively considering. Not being public, there were no issues.

Alternatively, go old school and bring the copies with you on an interview. This might be hard copy screenshots, or connect your laptop to their projector during an interview such that you always retain control over the material. Then, if you can't click-through to a certain portion due to it being an unreleased feature, patent papers not yet filed, etc., you have the control to navigate to away from there.

As another person commented here, some content on my personal website were anonymized screenshots organized as a storyboard; others were full replications of the entire system's UI and server, complete with documentation and including the original company's name & logo.

Sometimes the intent to have a portfolio begins when you start the project.

Depending upon nature of your project, you may be able to create it in a way that easily accommodates an anonymous version.

For example with one particular project, I kept all of the corporate colors and logos within CSS of course but intentionally kept it isolated to a single style.css file to make it trivial to change. It was essentially a "white label" system to accommodate re-branding, co-branding, etc. (Of course, no potential employer was interested in an end-to-end recommender system with mix & match algorithms-- think: compiling regular expressions-- so I've never shown that one-- oh, the irony!)

Even if you are concerned about nondisclosures and noncompete agreements:

You can demonstrate what work you have done despite most wording within agreements because they cannot prevent you from continuing to work within your field or prohibit you from earning a living after providing labor/services under those agreement-- with a few obvious caveats.

Those caveats include explicit statements about specific items to which you have agreed, and even in some of those cases, you may still be OK based upon local laws. But you should know when you're in that situation and would of course talk to an attorney and/or your original employer.