dhtmlxCombo can be used in four modes:
dhtmlxCombo is available in the Standard Edition only. Download and use dhtmlxCombo for free under GNU GPL, or buy a Commercial or Enterprise License to use the component in a non-GPL application/site and get official support.
Open Source - GPL - Allows the use of dhtmlxCombo in GPL-licensed projects for free.
Commercial License ($49) - Allows you to use dhtmlxCombo Standard Edition in one project (application) with an unlimited number of copies. The license includes 1 month of technical support (or 5 support requests within 12 months) and one major update.
Enterprise License ($99) - Allows you to use dhtmlxCombo Standard Edition in an unlimited number of projects on the condition that all of them are developed by one company. Free support/upgrades are provided for the first 12 months.
dhtmlxCombo Standard Edition is distributed under GPL v2, Commercial, and Enterprise licenses (details)