There is a particular startup for which I am a perfect fit: it’s in a niche, non-software, industry I’ve worked in for many years and I can safely say I’m the only person in the world with extensive experience in the industry who also is a very capable software engineer. Furthermore, I am in the process of building an open source tool poised to fundamentally improve the way the industry works, and the startup is building a paid version. My tool is of course a threat to their business. Even if their tool becomes higher quality, the presence of a free option is not good for their bottom line.So I think it makes sense to join them and either scrap my project or bring it to the company (not going to get into the specifics of which is a better option), but I think the situation warrants me being more than just an employee. I think it makes sense for me to receive a large chunk of equity. We could call this becoming another founder or not; I don’t really care about the title.One other catch: they already have three founders. Four seems like a lot.Does this seem like a reasonable proposal? Is adding a founder like this a common occurrence in startups? Any advice on how to approach the topic? Or any alternatives for someone in a position like this?