From looking at the comments here, it looks like it's very hard to make a living with a large open source project, especially if that project is an end-user app

From looking at the comments here, it looks like it's very hard to make a living with a large open source project, especially if that project is an end-user application. Most of the open-source code that I use are small, limited-scope libraries. These appear to come from someone who wrote the library as part of a larger project; and usually from someone experienced enough to make the library "good." Usually the limited-scope libraries solve a well-defined common problem that many applications need; instead of a unique tool that someone just wants to give away for free. Alternatively, there's frameworks like Spring that come from consulting companies. These frameworks only become valuable with lots of external users, so it's in Pivitol's best interests to sponsor their framework, which they also happen to be very good at using to write custom applications for paying customers.