Alert window example by Dockimbel

alert.red

alert: function [
    "Displays an alert message"
    msg [string!]  "Message to display"
][
    view/flags [
        t: text msg center return
        b: button "ok" [unview]
        do [b/offset/x: t/offset/x + (t/size/x - b/size/x / 2)]
    ][modal popup]
]