German manufacturer Invair has been attracting attention at CeBIT with its Filewalker PDA (personal digital assistant), which can be operated one-handed. To see images of the Filewalker, click here. Filewalker, which runs on the Linux operating system, lets users enter text by way of three buttons on the left side of its case, and a scroll wheel on the top. When held in the right hand the buttons are under the fingers, and the scroll wheel sits below the thumb. Text is entered by pressing the buttons, and users can turn the scroll wheel to change which three letters can be selected by the buttons at any moment. Invair claim that this makes their device ideal for people who need to access data when on the move. At 98g and slightly larger than a pack of cards, Filewalker has a 160x240 greyscale screen and a metallic case, so it's not as attractive as some of the other PDAs on show at CeBIT, such as the Fujitsu-Siemens Pocket LOOX. It offers decent functionality, though. When connected to a mobile phone by infrared it can send and receive email, and it also runs an address book, a calendar, a task list and some games. It can be synchronised with a PC running Microsoft Outlook and Exchange. Filewalker also has a multimedia card slot and a secure digital card slot, and runs on two AAA batteries. It is expected to go on sale in April for 649 euros (about £400).