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I've written a new task manager / system information app called "SystemPanel". It displays a list of running applications, and allows you to view information about them, e.g., memory consumption, when they were started, how much CPU time they've used since start, and so on. It of course provides "task killing" capabilities; it can end individual apps, all apps, or groups of apps such as "inactive" or "background" apps.
It also provides meters to show you current CPU consumption, network use, memory use, and SD card use. A "system info" function is available from the menu that provides all the gory details about your phone, everything from your Wi-Fi router's mac address to your Android build number.
A word of warning....SystemPanel does NOT offer a capability to automatically kill tasks in order to "save battery life". I disagree with the idea that such a thing would offer an improvement. The Android OS does a fine job of this all by itself, and such a capability would only be helpful if an app were suffering from a bug (or poorly written), such that is consumed battery unnecssarily in a semi-dormant state. And in that case, killing it every few minutes isn't going to solve the problem...one needs to uninstall it or contact the developer. If you happen to know a technically sound reason why such a task killing strategy is beneficial with well written apps, please let me know, and I'll be happy to rethink this. If you do want such functionality, there are tons of other task killers that supposedly have this feature.
Please feel free to post bugs / suggest features. At the time of this writing, 1.0b1 has just hit the market. It's been tested on Droid, Nexus One, G1, and a few emulators. It supports 1.5-2.1+, QVGA, HVGA, and WVGA.
Search for either "SystemPanel" or "NextApp" on the market.