WeightWatch - Weight Watch is an open-source application that allows you to track your body weight over a period of time.
This program follows the methodology brilliantly described by Paul Walker in his online book The Hacker's Diet, and attempts to mimic the usability and features of the applications found under the Computer Tools chapter of the same book.
Without going into a lot of detail, the idea is that there is an error of around 1~2Kg in each weighting on a regular scale, related to variations in the body composition during the day and imprecisions in the scale itself. In order to compensate for these errors, this program introduces a moving daily average in which radical differences in weight from one day to the next are smoothed over, resulting in a tendency curve. This is shown in a chart with the tendency curve bring "pulled" by the real weight measurements.
Though the curve may lag a little bit behind the real body weight, it reflects the tendency of the weight progress more accurately than the saw-tooth chart you would get with a simple day-to-day line chart. Paul explains the issue very clearly in the Signal and Noise chapter of his book.
This program was developed targeting Java-enabled mobile phones, but it should run anywhere where Java 2 ME is supported, which is to say, most mobile devices sold during the last 5 years.
Monthly chart showing daily moving average with floats and sinkers
Diet planner, drawn directly in the chart (the yellow line in the image above)
Adding new values (obviously)
Listing of old values
Cool sliding transition when changing charts between months
Incredible fade and 3D transitions between screens (where supported)
Graphical view of your BMI level, based on your height and weight