These allow you to use alternative formatting for your tiddlers. The
wikifiers are:

MediaWikiFormatterPlugin - allows Tiddlers to use MediaWiki (WikiPedia)
text formatting.

TWikiFormatterPlugin - allows Tiddlers to use TWiki text formatting.

TracFormatterPlugin - allows Tiddlers to use Trac text formatting.

There are (currently) at:

http://martinswiki.com/martinsprereleases.html

To use, just tag your tiddler with the appropriate tag. For example, to
use MediaWiki format in a tiddler, tag the tiddler with
MediaWikiFormat. To try it out you could create a tiddler, go to
Wikipedia and fetch the wikitext of an article, paste it into your
tiddler and then tag the tiddler with MediaWikiFormat.

Similarly, you could transfer wikitext to and from TWiki or Trac wikis.

Note that these are early releases and they are not complete. (For
example support for images in MediaWikiFormat is incomplete, as is
support for nested tables and templates). However I think they are
complete enough to be useful. I'd appreciate it if you post any bugs
you find in this group.

And for a bit of fun I've created a "TiddlyWikipedia" by posting a
number of articles directly from Wikipedia. See:

http://www.martinswiki.com/tiddlypedia/nordic.html

Note this is a bit slow to load. Note also that the rendering is not
perfect - I'm aware of this, but posted this anyway, since I think it
is a useful demonstrator and proof of concept.

Great wikifiers!  I will be definitely be using the TWiki formatter,
and I have already tried it out.  Can we make a way to globally enable
this for all tiddlers?  Can we make it possible to support both TWiki
and TiddlyWiki formatters at the same time?  What I really want to do
is be able to embed tiddlywikis as TWiki pages.  It can be done right
now by attaching an html page.  I may work on a TWiki plugin to enhance
this ability.

I don't understand all your questions though:

a) "Can we make a way to globally enable
this for all tiddlers?", do you mean can we make the default (say)
"TWikiFormat"?
This is actually quite tricky, since TiddlyWiki itself relies on
Tiddlers in standard format. I have a longer term plan to look into
this, though.

b) "Can we make it possible to support both TWiki
and TiddlyWiki formatters at the same time?". We already can. I expect
you mean: "Can you have TWiki and standard format in a single
tiddler?". This again is tricky, and in the the general case there are
formatting conflicts between different wikifiers.

But as a partial answer to (a) and (b) it would be possible to have a
pluging that supports as subset of TWiki format (the subset that does
not conflict with TiddlyWiki format) and have this "always on".

I already have a plan for a MediaWiki table formatter plugin, so that
you can use MediaWiki format tables within normal tiddlers. (I've
chosen MediaWiki format tables because they are by far the richest and
most powerful tables of any of the Wikis I have looked at. The also
have a nice syntax).

(c) <br> as line break. That's easy and I'll add it over the weekend.
(d) "the size of '---+' is really large...". I'll look into this, but I
presume it is just a style thing.

Here's a quick hack to help follow Wikipedia links which are not local
to the TiddlyWiki. Simply replace the defaultText with a link to the
Wikipedia article of the same name. Put the following in your
"settings" tiddler to get the idea.  (For a production version, you
would need to substitute '_' for spaces in the Tiddler name, %0.)

config.views.editor.defaultText = "See also:
http://www.wikipedia.org/wiki/%0";
config.views.wikified.defaultText="The tiddler '%0' doesn't yet exist.
Double-click to create it or click http://www.wikipedia.org/wiki/%0 to
view on wikipedia."

Your suggestion is a good one, and I'll incorporate it.