Seven companies including Mozilla, Arm and MontaVista have teamed up to develop an ultra-mobile PC - a device smaller than a laptop but bigger than a phone - that runs Linux.

The companies are collaborating on an open-source platform that encompasses chip design, operating system and some applications. They hope that it will make it easier for hardware developers to build devices similar to Nokia's N800 tablet. That Linux-based device is bigger than a smartphone but smaller than a laptop and includes Wi-Fi but not cellular networking.

The group, which also includes Texas Instruments, Samsung, Movial and Marvell Technologies, expects to complete the platform's development in the early part of next year, said Kerry McGuire, director of strategic alliances in Arm's connected mobile computing group. The devices should hit the market in early 2009, she said.

The device category is similar to the ultra-mobile PC but is based on Linux and not Microsoft software, said Jim Ready, CTO and founder of MontaVista.

Devices based on the new platform would weigh less than a laptop and might not require as many applications, he said. "You can attach to the web and do email and browsing without all the baggage of a PC and Windows and Office," he said. "There are web-based alternatives to all that." For example, instead of Microsoft Word, a user could access Google Docs online.

The group is "complimentary" to the LiMo Foundation, said McGuire. LiMo is one of many organisations working on specifications for mobile Linux. Those groups, however, aren't focused on this slightly different device category, said McGuire.

While the platform being developed may be similar to the one Nokia uses in the N800, the Arm group is creating a completely open platform that it will share with the open-source community, McGuire said.

The N800 has been available for a couple of years now, and Nokia has not discussed how many units it has sold. McGuire has high hopes for the category though. By 2010, she expects there will be 90 million of the devices on the market.

The platform will comprise Arm's Debian-based Linux distribution, MontaVista's operating system, a desktop and application environment from Gnome Mobile, a browser from Mozilla, a multimedia player and other components such as integrated hardware management for battery and power savings, a customisable user interface and various options for wireless connectivity.