# App Overview (/docs/line-21-app)



## When to use the app [#when-to-use-the-app]

The Line 21 App is a desktop application available for all major operating systems.\
It allows you to:

* Ingest audio from your computer (usually for [ASR](/docs/methods/asr) purposes)
* Produce [manual captions](/docs/methods/human) through your preferred CART software
* Display captions on screen through a customizable overlay

## Installation [#installation]

Line 21 is available for **Windows, MacOS, and Linux** (Debian/Ubuntu or AppImage).

  **Windows certificate** The Windows version currently has a temporary
  certificate issue. As a result, the operating system may show a warning during
  download or installation. You can safely ignore this message and proceed.

You can download the app directly from:\
👉 **[line-21.com/resources](https://line-21.com/resources)**

| OS                                                                                                  | Download Link                                                                                                                                                                   |
| --------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| <div className="flex items-center gap-2"> Windows </div>              | <a href="`https://line-21.com/api/assets?version=${DESKTOP_APP_VERSION}&extension=exe`" className="underline underline-offset-2 text-green-500">v{DESKTOP_APP_VERSION}</a>      |
| <div className="flex items-center gap-2"> MacOS </div>                  | <a href="`https://line-21.com/api/assets?version=${DESKTOP_APP_VERSION}&extension=dmg`" className="underline underline-offset-2 text-green-500">v{DESKTOP_APP_VERSION}</a>      |
| <div className="flex items-center gap-2"> Linux (Debian/Ubuntu) </div> | <a href="`https://line-21.com/api/assets?version=${DESKTOP_APP_VERSION}&extension=deb`" className="underline underline-offset-2 text-green-500">v{DESKTOP_APP_VERSION}</a>      |
| <div className="flex items-center gap-2"> Linux (AppImage) </div>           | <a href="`https://line-21.com/api/assets?version=${DESKTOP_APP_VERSION}&extension=AppImage`" className="underline underline-offset-2 text-green-500">v{DESKTOP_APP_VERSION}</a> |

## Project Code [#project-code]

Once the application is installed and launched, you must enter the **Project Code** to access its features.

Every project has a unique code shown in the main project dashboard, as illustrated below:

<img alt="Project Code" src="__img0" />

## Main Features [#main-features]

After entering the Project Code, the application provides access to three main features:

* **[CART Connector](/docs/line-21-app/cart-connector)** — Connect your preferred CART software and stream real-time steno input.
* **[Overlay](/docs/line-21-app/overlay)** — Display captions using a highly customizable on-screen overlay, suitable as a standalone display or as a video overlay.
* **[Direct Audio](/docs/line-21-app/direct-audio)** — Ingest audio directly from your system's audio devices.