There are many editors that support Fortran syntax highlighting.
(TODO expand this list)
Code::Blocks IDE for Fortran http://cbfortran.sourceforge.net/: Recommended! Originally developed for C++, this advanced IDE has many features of eclipse and supports most features of Fortran 2003 and 2008. The environment is quite user friendly and easy to use. It is one of the few true IDEs for Fortran. I think the support of the Fortran community will help this IDE to become a very powerful general purpose and fast Fortran programming tool.
Jedit - written in Java - when opening more than one file this has no tabs but a drop-down list at the top, which I find less convenient. But it has good Fortran90 aware syntax highlighting (I had to make a small change to the configuration file to prevent every line starting with C being treated as a comment, but that was not difficult). But the print system is a Java-special, not using the regular Windows print menu, so you can’t alter your printer defaults, e.g. to print 2 pages per sheet of paper. This is an annoyance.
Gedit - there is a windows binary to download which worked with no trouble, but there is no manual and no help (missing file). The syntax highlighting did work for Fortran90, but it did not understand the .f90 or .f95 file extension, and had to be set each time, which was very tedious. I could not find the relevant file on the website, nor when I untarred a regular gedit distribution. Looking at the help on a Linux box there did not seem to be a way of associating file extensions with language highlighting.
Notepad++ - has tabbed browsing, and uses regular Windows printing, but the syntax highlighting was set for Fortran77, and was really not useful. After being annoyed by it for some time, I found it best to disable the highlighting entirely. In principle one could define one’s own Fortran90 syntax file, but I couldn’t be bothered to do this. Apart from this it’s a fairly good editor.
Notetab light - the free version of a commercial editor notetab. This is another adequate editor: regular Windows printing, no tabbed file opening, no syntax highlighting. It seems to have no particular features that at least one of the others has.
Geany(http://www.geany.org/): This is a free open source editor with many capabilities which also supports programming in Fortran. There are several plugins to deal with project management, debugging etc. The editor lets you for extensive customization for a programming language and even adding new one! It is available for both Windows and Linux.
Simply Fortran(http://simplyfortran.com/): lightweight IDE for MS Windows and compatible operating systems. Made with GNU Fortran in mind, but configurable with most compilers, it comes with an intergrated development environment, a graphical debugger, and a collection of other development accessories. In early stages of development as of now, has some bugs, but the author’s working on them.
Programmer’s Notepad - A general source code editor for MS Windows. It can be configured to build Fortran files with arbitrary command lines, or to invoke make in a particular directory. Like many editors, it is C-centric, but the Fortran support is adequate.
Absoft Pro Fortran - A IDE developed by Absoft specially for Fortran. http://www.absoft.com/
FTranProjectBuilder - Fortran specific development environment for the Mac with built-in source code editor, makefile generator, and lab notebook. It’s Mac-native, self configuring and works with any Fortran compiler, including mpiXX for parallel computations. Fortran 2003+ features include variable and type bound procedure auto-completions. http://www.NocturnalAviationSoftware.com
UltraEdit - General source code editor for multiple languages with syntax checking. http://www.ultraedit.com. Runs on Mac, Linux and Windows 32 and 64 bit. There is a companion product called UltraCompare which allows one to compare files. Syntax checking is acheived through what the vendor calls word files. The vendor has a fairly good size library of wordfiles, but you can create your own if you wish. The Product also allows the developer to organize their work in a project fashion. Support for ftp,sftp, etc. Also allows column editing mode. I have been developing for decades and find this tool to be the best on the market when it comes to editors. Not a free product.
Visual Studio Code - To use VSC for Fortran on Linux I recommend installing the following plugins: Fortran Language Server, C/C++ for Visual Studio Code, Modern Fortran language support for VSCode, Fortran IntelliSense and Fortran Breakpoint Support.
findent indents fortran source, both fixed and free format. Conversion from fixed to free is also possible. Available for Linux and Windows. Plugins for vim and gedit are contained in the tarball at findent.sourceforge.net