Nice to know that xmlterm is still remembered (author). There is now an updated version, called GraphTerm, which is similar in some respects to Terminology but is written in python works completely within the browser.

To clear up some misconceptions, here's a response to some of the comments on Protozilla:

-Protozilla is not an "official" mozilla.org project. It is hosted at mozdev.org, as evident from the URL. (It is not the intent of Protozilla to delay the development of a viable Mozilla-based browser, which is proceeding at its own pace.)

-"Client-side CGI" is just one of Protozilla's features, and by no means the most important. As the name susggests, Protozilla is about implementing new protocols easily in Mozilla.

-Can the "client-side CGI" be used to maliciously access your local files etc.?

Protozilla is carefully designed to prevent this. The client-side CGI feature may only be used to execute files residing within the user's profile directory, which should be inaccessible to malicious web scripts. Furthermore, the request to execute the file is a special "restricted" URL which can only be loaded by the user typing it in in a special URL box (or from a privileged script). Unprivileged scripts downloaded from the web cannot load this URL. Nor can the URL be loaded by a "dumb" user clicking a malicious link on a web page. (Only executables which are specifically designated as implementing "public" protocols will be accessible to web page scripts through general-purpose URLs.)

However, any new functionality does open up the possibility of exploits and Protozilla is far from being fully tested/audited. So use it with care!

-Some posters on slashdot pointed out "prior art". These are useful to put Protozilla in context. Here are the links:

Pluggable protocol handlers in IE (http://msdn.microsoft.com/workshop/networking/plu ggable/overview/overview.asp)
Asynchronous pluggable protocols enable developers to create pluggable protocol handlers, MIME filters, and namespace handlers that work with Microsoft Internet Explorer 4.0 and later and a URL moniker.

W3M (http://www.gnu.org/brave-gnu-world/issue-16.en.ht ml)
A lot of browsers try to do everything in one program - W3M does exactly the opposite by calling external programs whenever possible. To make this easier it contains a "local CGI" mechanism that is capable of running CGI scripts locally without the help of a web server.

Jellybean (http://wgz.org/chromatic/jellybean.html)
Jellybean is a Perl Object Server with an HTTP interface, based upon an idea by Jon Udell.

MMM (http://pauillac.inria.fr/~rouaix/mmm/)
local CGIs [...] providing cheap and sophisticated MMM interfaces for applications.