EasyChat mentions sent directly to you via your os notifications.

easychat_os_mentions.lua

require("win_toast") -- you need https://github.com/Earu/gm_win_toast

local base_dir = "windows_mentions"
local function get_avatar(id64, success_callback, err_callback)
    http.Fetch("http://steamcommunity.com/profiles/" .. id64 .. "?xml=1", function(content, size)
        local ret = content:match("<avatarIcon><!%[CDATA%[(.-)%]%]></avatarIcon>")
       	success_callback(ret)
    end, err_callback)
end

hook.Add("ECPlayerMention", "windows_mentions", function(ply, msg)
	if not IsValid(ply) then
		WinToast.Show("Console / Invalid Player", msg)
		return
	end

	if ply:IsBot() then
		WinToast.Show(EasyChat.GetProperNick(ply), msg)
		return
	end

	local id64 = ply:SteamID64()
	local avatar_path = ("%s/%s.jpg"):format(base_dir, id64)
	if file.Exists(avatar_path, "DATA") then
		WinToast.Show(EasyChat.GetProperNick(ply), msg, avatar_path)
	else
		local function fallback()
			WinToast.Show(EasyChat.GetProperNick(ply), msg)
		end

		get_avatar(id64, function(avatar_url)
			http.Fetch(avatar_url, function(body)
				if not file.Exists(base_dir, "DATA") then
					file.CreateDir(base_dir)
				end

				file.Write(avatar_path, body)
				WinToast.Show(EasyChat.GetProperNick(ply), msg, avatar_path)
			end, fallback)
		end, fallback)
	end
end)