The DSi wasn't intended just for games; part of the meaning of the "i" is in reference to using it as a "personal tool," according to some Nintendo rep who may or may not have been full of it. We've already seen some fairly useless applications hit the service already, lending credence to this, so it makes a weird sort of sense for Nintendo to roll out applications for the musical crowd with Instrument Tuner and Metronome. And what do you know, they work well enough to possibly come in handy – if you carry your DSi with you everywhere you play, that is.
What we have here is a pretty standard metronome. You can adjust the beat and tempo by tapping some buttons on the touchscreen and up top is a pendulum bouncing back and forth to help you keep time. There are a few lights that keep track of where in the beat you currently are, with different colored lights for stressed and unstressed beats. The amount of beats you're able to set ranges from zero and one (all stressed or unstressed) all the way up to seven (the first being stressed), as well as the option of using between two and four eighth notes. It's pretty standard stuff that's good for practice, and unless you're in some strange odd-time experimental math rock band then you'll find the options plentiful.
Considering its basic job is to go tick-tock, Metronome adds a few nice touches, including the novel ability to record your own sounds for beats, three different skins (including a Game & Watch one) and a neat minigame called Donkey Kong Metronome that turns the first stage of the arcade classic into a rhythm game. The giant ape is up to his old tricks of kidnapping ladies and tossing barrels, so it's your job as Mario to get to the top of the girders and set things right by hopping barrels in time to the metronome. Movement is limited to jumps, which is done by creating a sound (be it from your instrument or just yelling at the thing), and your score is based on how close in time with the metronome you make the sound. Avoid getting hit and you'll hop up a girder; the beat starts off at a modest 90 bpm but increases with each one you reach. It's a more fun diversion than Tuner Fight and one that even those without an instrument or any musical abilities can get into.
One downside to the whole thing is that the sound is limited to the DSi's speaker volume, and while it should be alright for playing a guitar or some such by yourself we don't know how it would stand up against a loud drum set. You can always plug in headphones if it's too low, but then you have to have the DSi close enough to potentially get in the way unless your headphone cord is longer than average.
Those without instruments will find very little useful here (apart from the minigame, possibly), and those who are musical probably already have a metronome kicking around somewhere. Apart from the Nintendo touches, there isn't anything here that you can't get for free either online or on a smartphone, and splitting the metronome and tuner into two separate applications seems silly. What it does, it does well, so if you happen to be in the super niche market for an inexpensive DSiWare Nintendo metronome or always wanted to play Donkey Kong with an instrument or by clapping and yelling then look no further.