Business models for open-source software

Sell open source software commercially.

Use of dual-licensing to offer software under an open source license and other commercial (possible proprietary) license terms.

Attract customers by offering a free open source edition, then up-sell to a commercial enterprise edition.

Have open source software in your portfolio/offering to attract customers for your other commercial products and solutions.

Offer commercial technical support contracts and services.

Offering open source software in source code form only, while providing executable binaries to paying customers only.

Having the latest version available only to paying customers.

Offering commercial extensions/modules/plugins/add-ons to your open source software.

Independent developers often accept donations or sell swag.

SourceForge.net lets users donate money to hosted projects which have chosen to accept donations.

Partnerships with other companies.

Examples

Red Hat offers the Fedora for free through the Fedora Project, while selling Red Hat Enterprise Linux (RHEL).

Novell offers openSUSE for free, while selling SUSE Linux.

Sun Microsystems offers OpenSolaris for free, while selling Solaris.

Apple Inc. offers Darwin for free, while selling Mac OS X.

Francisco Burzi offers PHP-Nuke for free, but the latest version is offered commercially.

MySQL is offered for free, but with the enterprise version you can get subscription, support and additional features.

VirtualBox are sold as commercial proprietary software, but they also freely offer VirtualBox OSE, an open source edition.

Mozilla Foundation have a partnership with Google and other companies which provides revenue for inclusion of search engines in Mozilla Firefox.