Do there exist any outliners that do the composition part in HTML and not RTF? The reason I ask is because I want to keep a journal / general knowledge base and I need it to be very small and portable. If I could use tags to embed external images from the web instead of actually storing them in my database, then that would save a lot of space. This seems to be a brilliant feature, and I'm really surprised I can't find anything that will do it.

Any ideas?

You can use ConnectedText (www.connectedtext.com). You can create an outline and link topics to its nodes. Then you can export the outline to HTML including all text from topics, even images. No need to edit HTML. You will need to learn ConnectedText's markup commands.

Actually, there's quite a few outliners that use HTML for storing formatted text and images. It's just that they don't advertise the feature IMO. The question is, how easy do they make to edit the actual HTML source; otherwise images will probably be attached/saved along in the database, rather than be externally linked to.

From the tools I use, Surfulater utilises HTML but doesn't allow one to edit the source code; as far as I know, the same goes for UltraRecall which saves both HTML and RTF.

I think InfoQube is a good option, though I am still not proficient in it; I expect PPL (Pierre-Paul) who develops it to be able to provide more info.

Yet another option is Personal Brain, which is not exactly an outliner, but I remember it was very versatile in the attachment regard. All of its notes were stored in separate files and could actually be edited with an external editor from the file system. I haven't tried this in recent versions so its possible that things might have changed, but I suggest you give it a try.

InfoQube does let you do this, but so far I haven't figured out an easy way to edit HTML source, or a way to make the tree structure look very nice. It seems perhaps a bit over the top for what I want.

PersonalBrain does it and is a fantastic bit of software, but there is no security on the database at all! I see the request come up time and time again in the forums, and for them to have been around for 10 years and not add this is mindblowing. If it had password protection I would almost certainly be using it.

I'm just trying out ConnectedText now. Thanks for the suggestions. So far in my quest I have downloaded and trialled:
Treepad
MyInfo
Ultra Recall
MindRaider
Efficient Diary
Smart Diary Suite
EssentialPIM
TexNotes
My Notes Keeper
TreeDBNotes
myBase
WikidPad
InfoQube
Treeline
PersonalBrain

myBase+WebCollect stores Web pages as HTML and entered text and copied/pasted material as rtf. Both can be edited, although there are some limitations on the HTML editing. The HTML source code cannot be seen or edited as far as I know.
-c

Re Personal Brain: I would simply introduce password protection at the file system level. There's many utilities that do this. I personally use NomaDesk which syncs across my computers, providing me an encrypted drive when I'm not using it.

Re MyBase, mentioned by Cassius: I think it is an excellent option because, unlike other programs, it saves web information as separate internal attachments, i.e. .HTML., .PNG, .JPG files or whatever. I haven't used it since some versions back, but it should be possible to export, edit and re-import the HTML component.