First up is Quicksilver. If you don't know, Quicksilver is an OS X application launcher and much more. It basically allows you to open any application, document, or task using only the keyboard. It has a learning curve, but once you get the hang of it, it greatly speeds up your workflow.
There are two Linux alternatives I'll write about today, Kupfer and Synapse. Ubuntu's Unity and the new Gnome Shell have a similar feature built-in, but there's no reason those of us running Openbox or some other lightweight environment have to do without the snazzy features of a modern desktop. And Kupfer gets things off to a good start.
It's immediately familiar to Quicksilver users, and with its array of plug-ins pre-installed, comes with a lot of functionality out of the box. You invoke it with ctrl + spacebar or clicking on it in your system tray and then start typing and tabbing and arrow-keying. It's pretty intuitive. It has a fairly light memory footprint and a helpful preferences section where you can choose auto-load on login without having to edit config files. Imagine that.
Synapse is slightly different. It has a similar interface and comes with different skins, but it comes with less plug-ins built in and less functionality out of the box. Instead, it uses the Zeitgeist backend. Zeitgeist basically logs all your recent activity and how often you do certain tasks, and with Synapse utilizing it, can anticipate what you want almost before you type. Once you train it, Synapse just might be the more powerful in the long run. It's also fairly lightweight and has a similar preference panel where you can choose auto-launch on login instead of editing config files. Imagine that.
If they're both invoked with ctrl + spacebar, make sure they're not both set to auto-launch, though.
The only glitch I found (on both) was with drop shadows causing artifacts after the popup windows closed. I fixed it by adding f and -D1 options to my xcompmgr settings like this:
xcompmgr -cCf -D1
This adds fading and sets the interval to the lowest setting to make it imperceptible. That fixed it.
"This blog isn't dead yet!" he said screaming into the wind.