Based on the search results, "Appa Web" is not a known term or application. However, there is a popular messaging application called "WhatsApp Web". WhatsApp Web allows users to send and receive WhatsApp messages on their desktop computer or tablet. There is also an app called "Web Messenger for WhatsApp Web" available on the App Store. This app allows users to access the web version of WhatsApp and other messaging applications, and includes some advanced browser capabilities such as desktop view and changing user agent. Additionally, there is a YouTube video that explains how to log in to WhatsApp Web using your phone number. Finally, there is a security stack exchange post that explains what to do if you receive a message saying "WhatsApp Web is already open in another computer or browser".