It's a program offered by the company "The Get Your Act Back Company" and is mentioned as a potential solution for the protagonist, an extremely messy and unorganized man, to get his life back on track.
The company is a fictionalized representation of real-life companies that offer organization and decluttering services, but in the context of the book, "GWAB" becomes a symbolic representation of the protagonist's potential for change and the internal struggle he faces.