“I look at some of the investments made and I don’t get it,” said Michael Olson, the chief executive of Sleepycat Software, an open-source database vendor based in Lincoln, Mass., who advises several venture capital firms active in the open-source business.

Mr. Olson said that Sleepycat, which has never taken any venture money, has been turning a profit since 1996, charging other software makers an annual licensing fee to use its product.