A pointer from Mike Sax led me to venture capitalist Tim Oren's weblog entry about open source software as a business model. Oren raises the case of MySQL's two-track licensing: a GPL license for open source developers, and a commercial license for those who want to write commercial, non-open source applications with it. The commercial license protects developers against the “viral” nature of the GPL, meaning that anything they do with the code can be kept proprietary. (Novell recently acquired a commercial license of MySQL for its new version of NetWare.)

That's an intriguing approach–one I had been aware of before, but I hadn't really considered the the implications of it. The commercial license includes access to the MySQL JDBC, ODBC and C-based database access drivers from MySQL AB, which are not open source. Developers building pure open source applications can use MySQL freely under the GPL license; anybody who wants to tweak the code of MySQL itself has to buy a commercial license.

Again–the core is GPL; the tools to exploit the core for commercial purposes are not. Open source development is encouraged, while a revenue stream–the real revenue stream, in my mind–is maintained.