One of Canonical's main goals in bringing Ubuntu to mobile devices is to create a converged platform across smartphones, tablets, and PCs. As such, a developer should be able to write an app that has a single code base yet runs on all three types of devices, presenting a different interface to the user on each form factor.

Technically, this has already been achieved. Ubuntu Community Manager Jono Bacon this week showed off Karma Machine, a reddit client built by a third-party developer using the Ubuntu SDK:

Bacon also showed an earlier version of that app last October.

While that app can run across phones, tablets, and PCs, you won't actually find it in the PC version of the Ubuntu Software Centre right now.

Apps with the ability to run on all platforms "are currently available to Ubuntu for smartphones and tablets and will be available on the desktop when we release Unity 8 on the desktop at a later date," Bacon told Ars today via e-mail.

The Unity 8 user interface is already powering Ubuntu for phones, and it will power the version of Ubuntu for tablets expected to come in Ubuntu 14.04 in April. However, on the desktop, Canonical has decided to delay Unity 8 (and Mir, the new display server) until at least 14.10, which comes out in October.

There are security reasons for not making cross-platform applications available on the desktop software store yet, even though developers can make them available through other channels. Bacon explained:

We don't plan on shipping apps in the new converged store on the desktop until Unity 8 and Mir lands. The reason is that we use app insulation to (a) run apps securely and (b) not require manual reviews (so we can speed up the time to get apps in the store). With our plan to move to Mir, our app insulation doesn't currently insulate against X apps sniffing events in other X apps. As such, while Ubuntu SDK apps in click packages will run on today's Unity 7 desktop, we don't want to make them readily available to users until we ship Mir and have this final security consideration in place. Now, if a core-dev or motu wants to manually review an Ubuntu SDK app and ship it in the normal main/universe archives, the security concern is then taken care of with a manual review, but we are not recommending this workflow due to the strain of manual reviews.

The current goal is to get Unity 8 on the desktop in 14.10, "but we are always assessing our roadmap and reviewing what is realistic," Bacon wrote.

Cross-platform apps look pretty good on the desktop today, as seen in the above video, but they still aren't totally consistent with the look of other desktop apps. "We haven't finished optimizing them for desktop," Bacon wrote. "As an example, we want to handle menus, add right-click menus, scrollbars etc. That work is on-going. So, today they converge on phone and tablet, and they run on desktop, but in future apps will be optimized to run and feel like desktop apps more."

The other ambitious goal related to mobile/desktop convergence is Canonical's plan to let Ubuntu phones become a full-fledged PC by docking with a monitor, mouse, and keyboard. Just when this will become available is also unclear.

While users can download and run Ubuntu on certain Nexus mobile devices today, Bacon told Ars that Canonical is "not enabling [desktop docking] for the Nexus devices at this time."

No carriers or handset manufacturers have announced plans to offer Ubuntu devices, and Bacon has said he doubts any major OEMs and carriers will do so in 2014. The phone-as-PC docking technology likely won't become available until enabled by a manufacturer.

"This is a technology we have running now, but we are working with OEMs and Carriers to bring it to market," Bacon wrote.

Canonical unveiled Ubuntu for phones more than a year ago, saying that it was aiming to get a phone released in the last quarter of 2013 or first quarter of 2014. It doesn't look like that is going to happen, but Canonical's deep-pocketed founder, Mark Shuttleworth, has shown no intention of abandoning his dream of building a single operating system that can run on all devices.