If you have a pre-determined quota from your operator of how much packet data you can use in a month, it's a pain to first find the Logs application, open the packet data counter, then try and work out how much data you have left from the amount used so far. Data Quota shows two simple bars: one showing how much of the data for this month you have used, and one showing how much of the month has elapsed. This lets you tell at a glance if you've been using data up too quickly or slowly, so you can be more (or less) frugal.
Loanr is a simple loan calculator. It's been tested on primary BlackBerry devices and Symbian devices. It's handy to have when looking to purchase a car from a dealer with their frequent jumping back-and-forth from total payments to monthly payments, but also works for other types of loans and less low-pressure situations. The file is unsigned, and may illicit a warning on your device when you try and download it.
simplexbmcremote is a simple application for controlling XBMC remotely via the EventServer. It can navigate your collections, start, pause, and stop media, skip forward and backward, control the volume, and switch the subtitles. It is available on the Maemo5 (N900), MeeGo Harmattan (N9/N950), and Symbian^3.