Performance and System Apps
CPU tuner (Free)
CPU Tuner lets you regulate CPU speed, data connections, and syncing to help save battery power. You can create triggers based upon the battery level and the phone's status (locked, on battery or on power) to have it automatically adjust the CPU speed, data connection type and status, and background syncing. For instance, when your battery level is 30% or below you may want to under-clock the CPU to the lowest speed, cut back to 2G Internet or disable the cellular radio altogether. You can also toggle WiFi and Bluetooth through the app.
SD Speed Increase (Free)
SD Speed Increase tries to speed up transfers between your phone and the SD card. It modifies a system file to increase the cache size on the SD card from 128kb up to 2048kb. Though this cache size is reset on reboots, the app can automatically set it on every boot.
Android is only running on top of a barebones version of Linux. But you can get many of the standard Linux commands and Unix tools to work by installing this app. Install an app like Android Terminal Emulator to play with the new commands and tools through the command-line.