(users do not read! danger for brain!)
First of all I want to talk about abilities of native code.
Most applications built in inside WP7 are native. But they don't use usual Dialog UI style, they are using some kind of Silvelight scripts. This kind of UI is called "UIX".
Main idea of UIX that DLL files have UIX resources inside which describe whole UI.
Something similar is used inside CE 7.0 Slivelight - there some xml compiler which make binary data and put them as resources inside DLL. I don't know how to decode this binary data.
Seems Zune desktop application also using this framework.
So UIX used some kind of scripts for UI part and callbacks for all actions.
If we decode this UIX format, we will able to change/modify UI as we want, like it was before with regular resources inside DLL. But UIX must be much more powerful.
We can't use UIX for native application because we don't know how to use it, how to make proper binary data and etc. It's hard to reverse.
But native application can have some GUI with Windows CE style (you can see examples on the photos above)
Another issue: If you call API function "CreateWindowW" you won't see anything on the screen. It seems because shell handle all output, so window doesn't visible.
After some searching I found inside some test ROM nice DLL called "WindowTreeUpdater.dll
". After looking inside and decoding functions parameters, it's working!
Basic idea: you create window and call function from this DLL and Window appear on the screen. There seems some kind of proxy engine to output legacy windows on top of shell output.
Nice, it's working...
So we can use usual windows for UI inside native application.
There present standard controls, but they work rather laggy (hey, and looks too).
Basic controls like PushButton, Static, CheckBox, Radiobutton, Icon are working.
About extended controls: (Progress bar, list view, and etc)
they come from Commctrl.dll usually, it was present inside Initial/NODO releases, ut it was removed inside MANGO. I was able to run NODO Commctrl.dll under MANGO after some modifications. But all this controls are shown on screen, but they don't do anything on input. So you can see toolbar, but can't press any button.
CommDlg.dll is missing and never was inside WP7.
There present AYGSHELL.DLL, but most functions are broken. For example, I was not able to create menu bar.
So, a lot of functions are broken, like MessageBox not working.
But we still can create own custom controls and use them for developing.
For example porting TCPMP means that we will need reimplement UI fully - because toolbar doesn't work. slider also won't. Maybe get and reuse some source from ReactOS or NT40 CommCtrl