It started off as a "scratch an itch" sort of project: Rockwell Automation basically threw down the gauntlet when I asked them about Linux support and they responded that communicating with a PLC from Linux was not possible. I proved them completely wrong - first with the PLC5/SLC-500/Pyramid Integrator series, and then once again with the ControlLogix/Micrologix.
Profit wasn't the motive at first, then after I exited the industrial automation industry, it became a burden - a huge burden - to continue to support the packages. I also started to have a change of heart regarding the value of my time. I started off by asking for donations - and got absolutely nothing back. I then took the software off the free ftp server and got a total of 2 sales. Underwhelming to say the least.
As of today, I know personally of 2 different commercial software packages from 2 different software companies that are built on my software - as in sections copied verbatim (no, neither IBM nor SCO are involved there). Do I get so much as a thank you let alone a commission of any sort, nope.
Have I learned, you bet I have. My software packages today are commercial only with no source code available. It's a matter of survival at this point - gotta take care of number one first.