A company or organization may need a new or improved version of a software package, and fund some consultant or software manufacturer to do the work. Later on, the resulting software is redistributed as open source to take advantage of the large pool of skilled developers who can debug and improve it.
An example of this model is the work commissioned to Macadamian Software by Corel Corporation to improve the Wine Windows emulator. This work allowed Corel to port its entire software suite to several additional platforms (the suite was based in MS-Windows) with a simple recompilation process. This was of course significantly cheaper than accomplishing a complete porting process, or than building a proprietary Windows emulator, since Wine was already partially built. The work (still in progress) significantly improved the quality of the emulator, and the improvements made by Macadamian were integrated directly into the Wine code base.