Is there a directory of all the Mac Apps that support URL Schemes? A URL Scheme is a custom url that launches the app and might perform an action.
The above URL scheme works for OmniFocus.app
Another option would be to use
/System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/LaunchServices.framework/Versions/A/Support/lsregister -dump | grep -B6 bindings:.*:
For a list of all URL schemes the applications on your system support, get RCDefaultApp. It will add a preference pane to system preferences that includes a list of supported URL schemes and the applications providing that support.
Please note that these schemes are not necessarily related to useful services provided by the apps. Many exist simply to facilitate registering software (e.g.
webnote-license) by clicking a link in an email and aren't of any use otherwise. For the rest, you need to figure out how to use them. Just running e.g.
open txmt://foo in the Terminal will not produce a useful result.