PSPad is an amazingly powerful programmer's editor with a lengthy list of developer-friendly features.
A strong core editor includes all the goodies you'd expect: a tabbed interface, drag and drop editing, spell check (if you download additional libraries), case conversion, syntax highlighting, search/ replace in files and with regular expressions, block formatting and more.
But there's also plenty that might surprise you. An FTP client to edit documents directly on the server; smart HTML previews using IE or Firefox; an integrated copy of the TiDy library for reformatting HTML code; a macro recorder, and even a full Hex editor.
PSPad provides several ways to work with external programs. At a minimum, you can just run something, but it can also capture text output, parse logs and display the results for a real IDE effect.
You also get text differencing, matched brace highlighting, a code explorer, clipboard monitor, hash generator, expression evaluator, system file editor (view and edit HOSTS in a click), and more.
This all makes it easy to get lost, at least initially, but PSPad has more tools to help. A Projects system can be used to group related files together, while your open tabs and program state may be saved as a session, making it easy to continue where you left off later.
Version 4.6.1 (Changelog)
Scripting - new editor based function splitWindow([intetger]): integer. Returns or set editor window split: 0 - isn't splitted, 1 - split vertically, 2 - split horizontally
Search/Replace speed up
New action aFTPConnect (Shift+Ctrl+F) allows you connect to FTP with keyboard without mouse. It's available in the File menu, you can use it in scripting e.t.c.
Code explorer for STL - now parses functions with STRING [nn] parameter
Right edge line doesn't fit to ruller
File tabs - problem with whole text and high DPI (4k displays)
File change detection
FTP handles files with special chars in file name, e.g. FileName_14:33.txt
PSPad's interface is a little dated, probably because it's been around since 2001, and is now creaking with the sheer weight of its many features. The program isn't difficult to use, though, and if you need this level of functionality then PSPad could be a great choice.