Allow only RemoteApp, not Remote Desktop

There isn't an "officially sanctioned" way to do this because, fundamentally, TS RemoteApp functionality is just leveraging existing Remote Desktop code. You could do something silly like use Group Policy to set the user's shell to be "logoff.exe" such that if they attempted to access the machine's desktop they'd be immediately logged-off. Any application that uses a common "File / Open" dialog, though, can be used to get a command prompt or other programs open on the server's desktop.

You're better off making sure that you follow the principle of least privilege and give your TS RemoteApp users as few rights as they need to run the intended software. If they do end up on the server computer's desktop their restricted rights should prevent them from doing anything damaging to the server computer.

It is better to use "Application control policy" in the security settings just to allow only necessary applications or scripts if you use Windows 7 or Windows 2008 R2

This is what I have done to lock the Desktop to only be accessible for server administrators and a named AD group. Users that are not member of the given AD group will get a message telling them to use the RDWeb and not the Desktop/standard mstsc.

1. Create a vbscript and put it in a folder on the server that all users can read+execute

2. Add the following line to %windir%\system32\USRLOGON.CMD

   cscript <sourcefolder>\DesktopUserCheck.vbs
   

The vbscript code (please add your personal info in the below <> entries)

'Script created by Tord Bergset, Jan 2014
'This script is called from the file called C:\Windows\System32\USRLOGON.CMD
'The script check if a user logging on to the server desktop is a allowed to do this.
'The string called StrGroupName controls the access group to check for. 
'AD group used for this script = "G WTS Grant Desktop Access"
'---------------------------------------------------------------------------------------

Const strComputer = "."
Const EWX_LOGOFF = 0 

Dim objShell, objWMIService, colProcessList, objNetwork, StrGroupName, strUsername, strUserIsMember, strUserFullName

Set objShell = WScript.CreateObject ("WScript.Shell")
Set objWMIService = GetObject("winmgmts:" & "{impersonationLevel=impersonate}!\\" & strComputer & "\root\cimv2")
Set colProcessList = objWMIService.ExecQuery("SELECT * FROM Win32_Process WHERE Name = 'userinit.exe'")
Set objNetwork = CreateObject("Wscript.Network")
strUsername = EnvString("username")

' Mention any AD Group Name Here. Also works for Domain Admins, Enterprise Admins etc.
' -------------------------------------------------------------------------------------
StrGroupName = "G WTS Grant Desktop Access"
' -------------------------------------------------------------------------------------

If IsAdmin = 0 Then wscript.Quit

CheckADGroupMembership()

If strUserIsMember = "YES" Then
    ' Do something here if user is a member of the group
    'MsgBox "Is member"
    Wscript.Quit
Else
    ' Do something here if user is NOT a member of the group
    'MsgBox "Is not member" 
    For Each objProcess in colProcessList
        MsgBox "You (" & strUsername & " ) are not allowed to log in to the server desktop." & VBLF & "Please connect through the Remote Desktop Web Page (RDWeb):" & VBLF & VBLF & "<rdweb server address>", vbExclamation + vbSystemModal, strUsername & " - Access Denied !"
        objShell.run "logoff"
        WScript.Quit
    Next    
End If

Wscript.Quit 


' *****************************************************
'This function checks to see if the logged on user has local admin rights
Function IsAdmin()
    With CreateObject("Wscript.Shell")
        IsAdmin = .Run("%comspec% /c OPENFILES > nul", 0, True)
    End With
End Function

' *****************************************************
'This function checks to see if the passed group name contains the current user as a member. Returns True or False
Function IsMember(groupName)
    If IsEmpty(groupListD) then
        Set groupListD = CreateObject("Scripting.Dictionary")
        groupListD.CompareMode = TextCompare
        ADSPath = EnvString("userdomain") & "/" & EnvString("username")
        Set userPath = GetObject("WinNT://" & ADSPath & ",user")
        For Each listGroup in userPath.Groups
            groupListD.Add listGroup.Name, "-"
        Next
    End if
    IsMember = CBool(groupListD.Exists(groupName))
End Function

' *****************************************************
'This function returns a particular environment variable's value.
' for example, if you use EnvString("username"), it would return the value of %username%.
Function EnvString(variable)
    variable = "%" & variable & "%"
    EnvString = objShell.ExpandEnvironmentStrings(variable)
End Function


' *****************************************************
Sub CheckADGroupMembership()
    ' =============================================================
    ' List All Members of a Group; Including Nested Members
    ' =============================================================
    Dim ObjRootDSE, ObjConn, ObjRS, ObjCustom
    Dim StrDomainName, StrGroupName, StrSQL
    Dim StrGroupDN, StrEmptySpace

    strUserIsMember = ""

    Set ObjRootDSE = GetObject("LDAP://RootDSE")
    StrDomainName = Trim(ObjRootDSE.Get("DefaultNamingContext"))
    Set ObjRootDSE = Nothing

    StrSQL = "Select ADsPath From 'LDAP://" & StrDomainName & "' Where ObjectCategory = 'Group' AND Name = '" & StrGroupName & "'"

    Set ObjConn = CreateObject("ADODB.Connection")
    ObjConn.Provider = "ADsDSOObject":  ObjConn.Open "Active Directory Provider"
    Set ObjRS = CreateObject("ADODB.Recordset")
    ObjRS.Open StrSQL, ObjConn
    If ObjRS.EOF Then
        'WScript.Echo VbCrLf & "This Group: " & StrGroupName & " does not exist in Active Directory"
    End If
    If Not ObjRS.EOF Then   
        WScript.Echo vbNullString
        ObjRS.MoveLast: ObjRS.MoveFirst
        'WScript.Echo "Total No of Groups Found: " & ObjRS.RecordCount
        'WScript.Echo "List of Members In " & StrGroupName & " are: " & VbCrLf
        While Not ObjRS.EOF     
            StrGroupDN = Trim(ObjRS.Fields("ADsPath").Value)
            Set ObjCustom = CreateObject("Scripting.Dictionary")
            StrEmptySpace = " "
            GetAllNestedMembers StrGroupDN, StrEmptySpace, ObjCustom
            Set ObjCustom = Nothing
            ObjRS.MoveNext
        Wend
    End If
    ObjRS.Close:    Set ObjRS = Nothing
    ObjConn.Close:  Set ObjConn = Nothing
End Sub

Private Function GetAllNestedMembers (StrGroupADsPath, StrEmptySpace, ObjCustom)
    Dim ObjGroup, ObjMember
    Set ObjGroup = GetObject(StrGroupADsPath)
    For Each ObjMember In ObjGroup.Members      
        'WScript.Echo Trim(ObjMember.CN) & " --- " & Trim(ObjMember.DisplayName) & " (" & Trim(ObjMember.Class) & ")" & " (" & Trim(ObjMember.sAMAccountName) & ")"
        strThisUser = Trim(ObjMember.sAMAccountName)

        If lCase(strUsername) = lCase(strThisUser) Then 
            strUserIsMember = "YES"
            strUserFullName = Trim(ObjMember.DisplayName)
            Exit Function
        End If

        If Strcomp(Trim(ObjMember.Class), "Group", vbTextCompare) = 0 Then
            If ObjCustom.Exists(ObjMember.ADsPath) Then 
                'WScript.Echo StrEmptySpace & " -- Already Checked Group-Member " & "(Stopping Here To Escape Loop)"
            Else
                ObjCustom.Add ObjMember.ADsPath, 1  
                GetFromHere ObjMember.ADsPath, StrEmptySpace & " ", ObjCustom
            End If
        End If
    Next
End Function

Private Sub GetFromHere(StrGroupADsPath, StrEmptySpace, ObjCustom)
    Dim ObjThisGroup, ObjThisMember
    Set ObjThisGroup = GetObject(StrGroupADsPath)
    'WScript.Echo vbNullString
    'WScript.Echo "  ** Members of this Group are:"
    For Each ObjThisMember In ObjThisGroup.Members      
        'WScript.Echo "    >> " & Trim(ObjThisMember.CN) & " --- " & Trim(ObjThisMember.DisplayName) & " (" & Trim(ObjThisMember.Class) & ")" & " (" & Trim(ObjThisMember.sAMAccountName) & ")"
        strThisUser = Trim(ObjThisMember.sAMAccountName)

        If lCase(strUsername) = lCase(strThisUser) Then 
            strUserIsMember = "YES"
            strUserFullName = Trim(ObjThisMember.DisplayName)
            Exit Sub
        End If

    Next
    'WScript.Echo vbNullString
End Sub

run remoteapps WS2008 TS service en mac whit this client http://www.thinomenon.com/downloads/thinrdc-0.2.8.rar

work fine

You can take advantage of the fact that full user sessions launch the userinit.exe process while RemoteApp sessions launch the rdpshell.exe process. AppLocker can be used to prohibit userinit.exe from being executed by standard users.