Android only: If you're fairly sick of hearing your phone announce itself as a "Drooiiiiiid" or make other sounds during boot-up, Silent Boot is the handy single-use fix. It's an app that mutes your phone when shutting down, then un-mutes after boot-up.
That is all that Silent Boot does. It runs in the background, waits very patiently for your phone to start shutting down, and when it does, sets your system volume to 0/mute. After your phone boots back up, it sets the volume back to what you had it at before the shutdown.
Sure, it's a one-use app, but a helpful one, especially if you're tired of that geeky announcement. You can grab the app with the QR code at right or by searching out "Silent Boot" in the Market.
For other means of quieting your phone at boot-up, both with root access and otherwise, hit up Androinica's Silent Boot post, where we found this little utility.