I built these two nonsense Mac apps today because I wanted to practice some Obj-C/Cocoa. I don't usually build native apps, but I want to get into it more often.
The first is called epoch clock and it's pretty straightforward: just the current Unix epoch timestamp in red text inside a black window. You can click on the timestamp itself to copy it to your clipboard, or drag along near the edges to move it around. Very useful for nerds like me who deal with Unix timestamps all day. Download it here. It's based on a Processing sketch I built in college, but I wanted to recreate it without the Java overhead. In a future version, I may make a screensaver out of this.
The second is called passworder and, you guessed it, it generates random passwords using arc4random(). This is extremely similar to OS X's little-known built-in "New Password Item..." generator inside Keychain Access. However, this utility is a bit better: it allows you to specify a charset (I included a few basic ones, but you can edit the text field manually), the bit strength, a typical cliche strength indicator, and whatnot. You can just open it up and it'll launch with a nice secure 256-bit alphanumeric password. Download it here.