"Using Tcl/Tk to Rapidly Prototype Twilio-Powered SMS and MMS Sending Application" is a guide that demonstrates how to rapidly prototype an SMS and MMS sending application using the Tcl programming language and the Tk graphical toolkit. To start, you need to sign up for a Twilio account or use an existing one, purchase or find a SMS-capable number, and set environment variables such as TWILIO_ACCOUNT_SID, TWILIO_AUTH_TOKEN, and TWILIO_PHONE_NUMBER. The guide then covers the prerequisites for this tutorial, including installing required packages like tls, http, base64, and Tk. It also provides an example session in bash on Mac OSX 10.11.6 to clone the demo repository and run the application. The main focus of the guide is on creating a GUI with Tcl and Tk, then quickly sending out a text message using the Twilio APIs. The code includes functions like build_auth_headers, submit_form, and send_sms, which are reusable in other applications. The guide concludes by highlighting the possibilities of integrating communications into an application using Twilio's REST APIs, regardless of the programming language or platform used.