FileInfo.com - The File Extensions Resource

.STX File Extension

File Type 1	Scream Tracker Music Interface Kit File (Most common)
File Format	File
Common?	No
File Description	Audio tracker module file format published by Future Crew as a transitional format between the Scream Tracker 2 (.STM) and Scream Tracker 3 (.S3M) formats.
Program(s) that open stx files	Mac: CocoModX; MikMod Windows: MODPlug Tracker; MikMod; APlayer Unix: xmp module player

File Type 2	Pinnacle Studio Project File
File Format	Proprietary File
Common?	No
File Description	Project file created by Pinnacle Studio video editing software; contains video project settings and references to media and other data files used by the project. The STX file is typically saved in the same directory as the folder that contains the project data.
Program(s) that open stx files	Windows: Pinnacle Studio

Information from FileInfo.com - The File Extensions Resource.
http://www.fileinfo.com/extension/stx