TinyAlert is a lightweight (only 1.4k) alert system with Mootools and CSS3. Its easily customizable and bundled with few skins.

You can create your very own skins to match with your website or web application. You can also control the alert positions.

ReminderFeed is an online service (online) free program that allows alerts to read our favorite RSS reader.

It is very simple and practical, simply access the site, fill out a form that is similar to creating an agenda in any event such as the Google Calendar. Once the alert was created, we select our hours GMT and we subscribe.

Website: http://www.reminderfeed.com