PySimpleGUI, the simplest cross-platform Python GUI framework just added support for Repl.it (web in general) and it's the simplest way I've seen UI being done on Repl.it yet.
It has good autocompletion and it's well-documented. It's especially great for new coders that want to try their hands at coding GUI.
To get started simply import the library, create a window, and give it a layout! Here is a name reading app and repl:
import PySimpleGUIWeb as sg window = sg.Window('hello world').Layout([ [sg.Text('hello world')], [sg.InputText('enter name')], [sg.Submit(), sg.Cancel()] ]) [button, [name]] = window.Read() if button == 'Submit': print('Hello ' + name)