1990 Refilling toner cartridges for laser printers. I had someone else doing the refilling for me, so in terms of execution this was pretty much pure sales calls and I found that I wasn't good at that.

1992 A 1U rack mounted utility component for pro touring musicians that included a direct input (DI), tuner, metronome, front and rear rack lights, and surge protected outlets. NAMM attendees loved it. So did all the musician's that I worked with on the road at the time. But it turns out there's a lot to building physical products, especially ones that include custom electronics. We got a PO for 25 units from Guitar Center, but didn't have the chops to get it together and deliver. In the end it came down to capital and we had none left.

2000 A SaaS solution (then known as an ASP) for project management for commercial construction. Not sure what went wrong here. Probably lack of sales competency. A peer and competitor at the time, eBuilder, just sold for $500 million 2 years ago. That was a long ride. We shut down in 2008.