This online application is free and designed to convert GPX to KMZ file format. The KMZ format requires less space than KML. This format is a good choice for transferring geo data over the Internet. However, for geoprocessing tasks, KMZ is suboptimal because it takes time to unzip.
Conversion App is a free application provided by Aspose.Gis
GPX extension represents GPS Exchange format for interchange of GPS data between applications and web services on the internet. It is a light-weight XML format that contains GPS data i.e. waypoints, routes and tracks to be imported and red by multiple programs. GPX is open and is supported by variety of applications and GPS devices.