The URI schemes page on Wikipedia has an entry for "apt:", which is used at least by Ubuntu AFAIK. So, "apt:<packagename>" would be really short for packages that are in Extras. Maybe we could also special-case the situation where <packagename> is not in Extras (and check for Extras-Testing/-Devel and ask the user with a big, fat warning if (s)he wants to install unstable software?).

For "single deb" installation, we could either detect ".deb" at the end of an URL and assume it's a package (maybe asking the user first) or "invent" some pseudo-URI-scheme (e.g. "dpkg://", which will be used to "detect" an installation request, and "dpkg://" will be replaced by "http://" before trying to download the package - "dpkgs://" could be used for https:// URLs).

Or maybe we leave the single-.deb option completely out of this as an incentive to get apps into Extras and just go with "apt:" URIs?

We could (if we wanted) support repository information by adding the parameters at the end of the "apt:" URI, e.g.:

apt:feedingit?url=http://repository.maemo.org/extras-devel/&distribution=fremantle&components=free%20non-free