Phonegap and Titanium are different things from jQuery Mobile and Sencha Touch, which are slightly different form jQTouch.
Want to build a complex app that could run on iOS, Android and Windows Mobile with no(t much) fuss? Don't like writing HTML or CSS by hand but enjoy writing JavaScript MVC stuff and fancy learning new stuff? Go with Sencha.
Want to build a nice mobile interface for a website but you need your very own markup and CSS and you'd also like to apply your jQuery king-funess to the project? jQuery Mobile is the thing you need.
Want that "site" to be a native app that talks with your web services and uses accelerometer, gps and camera? Add Phonegap.
... or appMobi/jqMobi. You could basically use of any of these frameworks/libs and run your project through appMobi in the same way you would run it through Phonegap.
Want to build a complex app that could run on iOS, Android and Windows Mobile with no(t much) fuss? Don't like writing HTML or CSS by hand but enjoy writing JavaScript MVC stuff and fancy learning new stuff? Go with Sencha.
Want to build a nice mobile interface for a website but you need your very own markup and CSS and you'd also like to apply your jQuery king-funess to the project? jQuery Mobile is the thing you need.
Want that "site" to be a native app that talks with your web services and uses accelerometer, gps and camera? Add Phonegap.