The DataSelf Desktop is another name for the Tableau Desktop app. In the past, the DataSelf Desktop app was modified to work exclusively with the DataSelf system. In 2023 Tableau has discontinued the modified versions of the Tableau Desktop, so all installations of Tableau Desktop after that are the standard Tableau version.
DataSelf/Tableau Desktop is installed locally on your computer, (it is not a web app), and must be registered/licensed on your computer in order to use. It is a named user license, not generic.
Link to download & install reference:
Download, Install Tableau Desktop and Server - DataSelf - Confluence (atlassian.net)
Links to Tableau help article on differences between Tableau Desktop and Web Authoring:
Web Authoring and Tableau Desktop Feature Comparison - Tableau
Tableau Desktop v Tableau Web Editing
Tableau file extensions definitions, *.twb and *.tds Files
Tableau WorkBooks (*.twb)
Tableau Packaged Workbook (*.twbx), (Tableau WorkBook Extract)
Tableau Data Source (*.tds)