Webvoice is a text to speech cgi program. You can embed a link in a html page to send things you want to say, via sound. No software is required on the client side. Festival and sox are needed on the server. Webvoice has its own interface (if needed).
The Lazybones project is a server and a collection of clients. It allows one person to voice control multiple machines. Designed for software developers and sys admins, Lazybones speeds up redundant and/or complex tasks.