Unfortunately Borland didn’t implement a public register and start function into the class TServiceApplication. So we have to do it ourselves.
First we publish the protected RegisterServices function to allow (un-)install our service(s) programmatically.

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It is impossible to use SetThreadDesktop and the VCL at the same time because a thread can only show windows on one desktop at a time. However VCL is not written for the use with multiple threads, so there is no way to show Delphi forms of same process on two different desktops. SetThreadDesktop [...]

This answer is very easy – just use GetWindowThreadProcessId
JWA declares it as followed:
function GetWindowThreadProcessId(hWnd: HWND; lpdwProcessId: LPDWORD): DWORD; stdcall;
The function returns an identifier (not a handle) and also may set lpdwProcessId to the identifier (again not a handle!) if it is not nil. Be aware that identifiers aren’t handles, so you must not close them [...]

Please read this “How to” before submitting any Header Conversions to us.
Then you can submit the headers to us by mail.

The JWSCL does only need a minor setup. You need to create a binary unit file (DCU-file) for the JEDI API Headers as described here.
You must setup JEDI API first before you can start with JWSCL! Otherwise if you set Delphi source path to include JwaWindows.pas you’ll get an error like:
Incompatible types: JwaWindows.XXX and JwaWinNT.XXX
JWSCL [...]

The JEDI API library provides you two ways of using it. Either you can use all the single units like JwaWinUser.pas and JwaWinTypes.pas or you can use just one unit that includes all these single units. It is called JwaWindows.pas. The
1. Single units use:
Single units are included into your project by adding the JEDI [...]