The “geo:” specification has become stable, and implementation of the first few applications is underway. The following applications / software / sites do already support “geo:” URIs:

• Android supports a “geo:” intent, however, the implementation is based off a very old draft version of the specification, and includes some proprietory extensions. It does not seem to support altitude.
• Perl module “URI::geo”: The module allows creation and parsing of “geo:” URIs from within Perl.
• Firefox: An (outdated) extension for older versions of the Firefox browser is available here.
• Chrome: A proof-of-concept extension for Google’s Chrome browser can be found here.
• Python Package: Work on a module for Python has been started here.

We’re looking forward to more applications (and we’re aware that some are already underway). If you did an implementation (or plan to do so), please post a comment – we’ll update the list.