#1 - Two of us. A package for specialty manufacturers. I wrote the software, he sold and implemented it. We agreed to make it a product business, but he sold it as a service. Totally different animals. We were always behind and had no chance of building any equity that way.
#2 - Four of us. A package for continuous manufacturers. I was one of 2 programmers along with a designer/analyst and a business guy. I should have been spending all of my time programming, but I spent 75% of it refereeing among the other 3. I kissed the ground when I left.
#3 - Two of us. A package for job shops. Things were just taking off when he died.
#4 - I'm taking everything I've learned from the other businesses and from my customers over the years and writing a self-service web app that builds enterprise quality systems for small & medium businesses. Single founder is the default. I'd gladly have a co-founder or two, but only if the fit is (almost) perfect. One of the many reasons I came to hn was the possibility of meeting co-founder(s). Who knows, it still may happen...