.ARIA2 File Extension
What is an ARIA2 file?
Control file format created and used by aria2, a command-line download utility; stores the progress information of a download; not meant to be opened.
The ARIA2 file is placed in the same directory as the downloading file and has the same name as the file being download except it has the "aria2" extension appended. For example, when downloading the example.pdf, the file appears as example.pdf.aria2. Once the download is complete, the ARIA2 file is deleted.