ATV is a display and quick-look analysis program written in the IDL language for use with astronomical FITS images. It is free to download and use, but using IDL requires a license. You can download the program and find instructions for installation and use on the ATV web page.
I have very little time these days to update and improve ATV, but I do try to fix bugs when they are found. If you are having trouble using ATV, the most common reason is that your supporting libraries (the IDL astronomy users’ library and/or the Coyote library) are out of date or out of sync with each other, so that’s the first thing to check.