One of my latest favorite discoveries in the Android market is aLogcat, a must-have for Android developers and power users, who want to know more about what is going on on the device. It is named after the logcat command which can be run in the debug shell, typically via the adb tool from the Android SDK, which requires the device to be connected to a host PC through a USB cable.
aLogcat allows to display a log console on the device itself, color coded by levels with options to filter by levels or arbitrary substrings. By default the console updates continuously with new messages as they appear in the log, but it can also be frozen to allow scrolling back through the log history without interfering screen updates. Since logs can also be sent via email, it subsumes the functionality of earlier log collector apps.
Now that the number of devices, configurations and version of Android are exploding, it is less and less likely that a developer can reproduce a particular problem, since they may only occur in particular device configurations to which the developer does not have access to. Tools like aLogcat are often the only way how developers can remotely diagnose a problem, with the help of a user who can reproduce it and is willing to invest some time in getting it resolved.