When properly used, a Domain Specific Language or DSL can drastically reduce development time. Unfortunately, editing DSL files usually has to be done manually with simple text editors like Notepad. This is where Notepad++ comes in.
Notepad++ is a lightweight code editor that supports a impressive list of languages including C, C++, Java, C#, XML, HTML, PHP, Javascript, RC resource file, makefile, ASCII art file (extension .nfo , screenshot1, screenshot2), doxygen, ini file, batch file, ASP, VB/VBS source files, SQL, Objective-C, CSS, Pascal, Perl, Python, Lua, TeX, TCL, Assembler, Ruby, Lisp, Scheme, Properties, Diff, Smalltalk, Postscript, VHDL, Ada, Caml, AutoIt, KiXtart, Matlab and Verilog.
Additional languages can be added using a fairly intuitive dialog. John Galloway demonstrates this by adding the PowerShell syntax to Notepad++.
Notepad++ supports modern code editor features such as code completion and macros, but it is not a full IDE. This is an open source project and can be downloaded from SourceForge.