I currently use a Windows-only application called As-U-Type, a text expander. (Similar products are Vellosoft Superkeys, which may be out of business, and ActiveWords.) It's kind of like AutoCorrect in OpenOffice.org, but (a) more powerful and customizable, and (b) independent of any particular application; it works the same whether I'm in WordPerfect, Opera, or anything else. It's very important for my work, which among other things involves typing SGML codes into a Web form.

As far as I've been able to tell so far, there is no Linux equivalent. If you can tell me I'm wrong, I'll be grateful.

Because Linux GUI-based apps use a variety of different libraries for drawing the basic widgets which make up the interface, I think it's unlikely that you will find something which works for all apps.

You might be able to find something which works for all KDE apps, or all gnome apps, although I don't know of one. Having said that, I never looked for one, so there may be something around.