MapBasic Editor
The MapBasic Editor is a very simple text editor that quickly gets too simple if you really want to do a lot of programming.
The first limit that you'll run into is the size of your source files. The Editor can't read files larger than 64 KB, which isn't that much.
On the good side, you'll see that the editor is well integrated with MapInfo, which makes it easy to run a application from the editor in MapInfo simply by using the shortcut Ctrl + U.
After a while you'll be looking for an alternative editor, and you'll quickly find some other nice editors that might not be that well integrated with MapInfo, but on the other hand, they give you a lot of tools when dealing with text editing.
An interesting editor is UltraEdit, which is used by a number of famaous MapBasic developers on MapInfo-L. UltraEdit is a very strong Editor, that gives you some powerfull tools for handling source code.
Another interesting tool is DiaBuilder 2000 that will help you create dialog visually.