from tkinter import *
import win32gui
import time

root = Tk()

root['bg'] = '#fafafa'
root.title('Название программы')
root.wm_attributes('-alpha', 0.85)
root.geometry('300x250')

#текстовое поле
ent = Entry(width=20)
but = Button(text="Преобразовать")
#lab = Label(width=20, bg='grey', fg='white', )
labName = Label(width=20, bg='grey', fg='white', )

ent.pack()
but.pack()
labName.pack()

def windowsName(event):
    tempWindowName = win32gui.GetWindowText(win32gui.GetForegroundWindow())
    labName['text'] = tempWindowName
    root.title(tempWindowName)

but.bind('<Button-1>', windowsName)
root.bind('<Return>', windowsName)

root.mainloop()