About $300/month from a GPL script. A PHP class, quite popular, about 7 years old and still going strong. I am surprised nobody in this thread gets recurring income for sharing open source code. I mostly receive donations. I also sell licenses, from a few dollars to hundreds. I publish about three releases a year, and don't spend that much time working on it or supporting it. I shall not forget to mention that publishing this code got me a lot of freelance gigs. Bonus fact: it is rather enjoyable to go to a contract interview where the interviewer has actually used my code.