I used to be a solo dev working in a niche field where I made plug-ins for some creative apps. I found that one thing that really helped was being active in the

I used to be a solo dev working in a niche field where I made plug-ins for some creative apps. I found that one thing that really helped was being active in the forums where users were, and (if allowed by the forum) posting that you have a product and you'd like to get some people to test it. I'd then require them to fill out a simple form that gathered some information about how they work. The form served 2 purposes: 1) It gave me the ability to balance different types of users. Hobbyists vs. professionals. People in this specialty vs. that specialty. etc. 2) It weeded out people who just wanted something free and weren't interested in giving feedback. Seriously, a simple form requiring a name, an email, and the answer to 3-5 questions helped get rid of the freeloaders. But don't make it too onerous or you won't end up with any testers. I'd then usually give a free license for the released product to anyone who provided useful feedback.