What concrete steps can I take to make money on the side as a software developer?

My humble advice,

Forget about critical mass!

If you need critical mass to success and if you are not hostshot blogger or buddy with some well known press guys you'll almost never reach a critical mass.

Don't follow every single rabbit you see

A Russian proverb:

"If you chase two rabbits, you will not catch either one."

Find something and stick with it. I know you got tons of good stuff, but find the best, run it with your friends, chose one of them, believe in it and stick with it.

Find your powerful skill and built your project on it

Do you have any unfair advantage? Use it.

If you are just interested in making extra money on the side, a service based business could work for you. Think about areas such as the following:

• Custom modifications for existing platforms - e.g. Wordpress
• Custom development - e.g. Via freelance sites or word of mouth
• Niche hosting or administration of specific applications
• Content creation - e.g. blogging or education content

You'll hit against the same challenges in terms of marketing and building traction or critical mass, but this will be without the overhead of product development. (There is probably a lot to be said for learning sales & marketing within a service business.)

If you are determined to go the product route, consider making your development process much more customer led. In short, don't build products that people don't want, instead putting the effort into up-front customer research and validation of your idea. To quote Jason, if you can't get people to even talk about your idea, it's a slimmer chance you'll actually get people to buy it.

I more and more believe in David Heinemeier Hansson philosophy of selling small and simple apps. You have to concentrate on small business because consumers don't usually pay, when they start paying stop and big business tend to be hard to sell to.

I recommend watch The Secret to Making Money Online. I'm really passing on advice that I've got as I haven't had the chance on acting on it yet, but the next time I have free time, I will.

This have been said many, many times; but after experiencing myself I consider it's worth repeating: get a partner. I worked on many projects by myself, I have ideas constantly, as soon as a project looks like it's not working, I move to the next idea. With a partner you don't do that. With a partner you don't stop. With a partner you pick what you have and tweak it and change it and try to make it stick again, and again, and again.

You are doing this on the side, so I wouldn't call it "partner", just a "programing buddy" or whatever. Get the idea, go to a friend programmer and tell him whether he would like to work on it, just for the fun, and if there's any money, you'll split.

Have a partner to share the whole experience.

I find having a partner or friend, who is involved in the project with me can really help keep up my enthusiasm and excitement. However finding good friendships and partners can be difficult especially in a smaller area. User groups and coworking meetups are always a good place to find "entrepreneurial" people who usually want to have that successful side project.

Your core competency is your software development skills which allow you to build useful software. The fact that your software projects don't take off may have nothing to do with the software but rather the marketing and selling of your software which is a very different skill set.

Having been in a similar situation as you I believe the best thing to do is to find someone as ambitious and pationate about promoting and managing your software as you are about creating it, and make them a partner/co-founder.