Fortran has language-level support for things important for numerical scientific computing (complex numbers, multidimensional arrays, etc.), and it has had them since the beginning in the 1950-60s.

The convenience is not really matched by C or C++, where similar features have been added much later by language extensions or 3rd party libraries, resulting to more complicated usage, fragmentation, and interoperability problems. Newer languages also have similar issues, so for the user base that uses Fortran, there's a lack of viable competitors.

I write mostly C++ and Scheme and last year I wrote my first piece of code in modern Fortran (I had some experience porting/integrating old F77 libs). It's trivial to interface with C and lets you do numeric stuff immediately and without libraries using a plain syntax. Compared to C++ with template array libraries it compiles much faster and doesn't get in your way nearly as much. It has a module system... Compared to numpy/matlab/etc it takes some adjusting b/c it's still a lowish level language (errors lead to segfaults, etc.) but a lot less than going to C/C++.

It's still around in the high-performance scientific computing world. Feature-wise, C99 basically looks like playing catch-up with Fortran to better compete in that space (eg restrict, complex numbers, type-generic math functions, stack-allocated variable length arrays).

Every time Fortran is mentioned, this seems to come up. In one thread I referred to the usage figures for the UK "tier 1" system, for instance.

It's used in science (physics, chemistry, astronomy etc). Just like C++ is used not because it's a nice language but because of inertia and path dependecy, the same goes for fortran.