What is a .dbf file?

A .dbf file was the underlying file format of dBase (published 1980), one of the first database management systems for personal computers. Back then, dBase was the most successful database system. The DBF file format was not only used by dBase itself but other programs used it as a local database.
After 2000 the interest in dBase started to decline, but there are still niches in which the dBase file format is used today. For example, the shapefile format uses .dbf files to store GIS data.

And what is this service good for?

Lots of programs can still open .dbf files, such as LibreOffice, which might already be installed on your computer. However, the support for this ancient file format in desktop application decreases and at the same time new plattforms like tablets or phones do not offer any built-in possibilities to open a .dbf file.
To solve this problem DBFopener.com offers a way to open a .dbf file via the browser without installing an app.