I've written before about Enso, a very interesting project that lets you perform tasks from a command-line that interacts with the user interface. The software comes with some basic commands (like launching programs, performing calculations), but it can be extended with other commands. Enso has recently launched in beta some plug-ins that add new commands.
Let's say you need to translate into French some text from an email message you're composing in Gmail. You'll have to select the text, open a new window or tab, go to Google Translate or other translation service, paste the text, choose the option to translate from English to French, click on a button, select the translation and copy it, go back to Gmail and paste the text. The new translation commands for Enso let you perform the same task much faster: select the text, trigger the command line (press Caps-Lock), type the first letters from the command ("translate to French") and the translated text will replace the selected text. Of course, you won't get a more accurate translation, but at least you won't lose the original context and get distracted by other tasks.
The search commands let you select some text and type the name of one of the supported search services to launch a new page with the corresponding search result. This is faster than using your browser's search features or extensions like Hyperwords because you don't have visually identify the right option from a long list. Unfortunately, these commands defeat the one of the main purposes of Enso: don't lose the context. An alternative way to implement them would be to use APIs like Google AJAX API to display search results without leaving the page. In fact, my favorite use of this API is a tool called Linkify that allows me link to a search result by selecting some text from a textarea and choosing one of the search results displayed in a small sidebar.
There are also commands for controlling music players or to convert LaTeX markup into a nice mathematical expression. Of course, an API would make it easier to build many other plug-ins for Enso.
For now, Enso works only on Windows 2000/XP/Vista and the main program costs $20 (there's a 30-day trial), while all the plug-ins described above are free. I think a better approach would be to pay for some additional commands and make the main program free. When you can find a lot of great software like Google Desktop, Launchy, Quicksilver, Foxytunes, I'm not sure many people are going to pay for Enso.
The software comes from a small company called Humanized that promises "to provide you with the most humane software we are capable of making". Great interfaces, easy to use software, simplicity - I've heard these things before (I wonder where?).
"Some tasks—for instance, teaching a child arithmetic—are intrinsically pretty complicated. But some aren't. Setting the time on a wristwatch, for instance, shouldn't be that hard; on old analog wristwatches, it basically involved pulling out a knob, twisting it until the watch showed the correct time, and pushing the knob back in again. But on newer digital wristwatches—ones that claim to be more powerful and feature-loaded than their analog counterparts—it involves pressing a series of buttons in a hard-to-remember, often unforgiving order. Most people dread setting the time on their digital watches, and for good reason."