LineOne's notifications: a small colored note at a corner or an edge of the screen that leaves by itself after a few seconds.

Mount the toaster once, in the layout every LiveView renders (it reads the flash):

<.toaster flash={@flash} />

Then, from the server:

conn |> put_toast("Saved", color: "success") |> redirect(to: ~p"/orders")
socket |> put_toast("Saved", color: "success") |> push_navigate(to: ~p"/orders")
socket |> send_toast("Copied", color: "info", position: "center-top")

put_toast/3 goes through the flash, so it survives a redirect; send_toast/3 pushes the toast to the page at once. From the browser, without a round trip:

<.button phx-click={show_toast("This is a simple notification", color: "primary")}>Primary</.button>

Options: color (neutral primary secondary info success warning error light dark), position (left-top left-bottom center-top center-bottom right-top right-bottom), duration in milliseconds (0 keeps it until closed), close (a close button) and template, the id of a <template> on the page whose first element is shown instead of the message (an element with data-toast-dismiss inside it closes the toast).

The toasts of a corner are stacked: the newest is shown in full and the older ones sit behind it, smaller, as slivers (three at most). With the pointer over the stack it opens, every toast in its own size, and their timers wait; when the pointer leaves they go on with the time they had left. Set stack={false} on the toaster to keep them always open, one above the other.