Hide the Sidewise icon from the Windows taskbar and take it out of the alt-tab list.

SidewiseTaskbarHider.ahk

;#NoTrayIcon   ; uncomment this to also hide this script's systray icon
init()
return

init() {
    ; Configure event hook for window-created message reception
    Gui +LastFound
    hWnd := WinExist()
    DllCall( "RegisterShellHookWindow", UInt,hWnd )
    MsgNum := DllCall( "RegisterWindowMessage", Str,"SHELLHOOK" )
    OnMessage( MsgNum, "ShellMessage" )
    HideSidewise()
    return
}

HideSidewise() {
    title := "Sidewise ahk_class Chrome_WidgetWin_1"
    if (!WinExist(title)) {
        return
    }
    WinSet, ExStyle, +0x80, %title%  ; hide from alt-tab order
    RemoveWindowFromTaskbar(title)
    return
}

RemoveWindowFromTaskbar(WinTitle) {
    /*
      Example: Temporarily remove the active window from the taskbar by using COM.

      Methods in ITaskbarList's VTable:
        IUnknown:
          0 QueryInterface  -- use ComObjQuery instead
          1 AddRef          -- use ObjAddRef instead
          2 Release         -- use ObjRelease instead
        ITaskbarList:
          3 HrInit
          4 AddTab
          5 DeleteTab
          6 ActivateTab
          7 SetActiveAlt
    */
    IID_ITaskbarList  := "{56FDF342-FD6D-11d0-958A-006097C9A090}"
    CLSID_TaskbarList := "{56FDF344-FD6D-11d0-958A-006097C9A090}"

    ; Create the TaskbarList object and store its address in tbl.
    tbl := ComObjCreate(CLSID_TaskbarList, IID_ITaskbarList)

    activeHwnd := WinExist(WinTitle)

    DllCall(vtable(tbl,3), "ptr", tbl)                     ; tbl.HrInit()
    DllCall(vtable(tbl,5), "ptr", tbl, "ptr", activeHwnd)  ; tbl.DeleteTab(activeHwnd)
    Sleep 3000
    DllCall(vtable(tbl,4), "ptr", tbl, "ptr", activeHwnd)  ; tbl.AddTab(activeHwnd)

    ; Non-dispatch objects must always be manually freed.
    ObjRelease(tbl)
    return
}

vtable(ptr, n) {
    ; NumGet(ptr+0) returns the address of the object's virtual function
    ; table (vtable for short). The remainder of the expression retrieves
    ; the address of the nth function's address from the vtable.
    return NumGet(NumGet(ptr+0), n*A_PtrSize)
}

ShellMessage( wParam,lParam )
{
    WinGetClass, Class, ahk_id %lParam%
    WinGetTitle, Title, ahk_id %lParam%
    if ((wParam == 6 || wParam == 1 || wParam == 2) && (Title == "Sidewise" && Class == "Chrome_WidgetWin_1"))
    {
        HideSidewise()
        return
    }
}