Summer is upon us! The days are getting longer, the sun is out, and the view outside the window is making it difficult to stay indoors. Fortunately, more than a few free applications are just waiting for the chance to use your idle computer time for good.
(For links to all of these programs in one convenient list, see our "Free Downloads to Make Use of PC Idle Time" collection.)
Many people set their computer to put up a screensaver when they leave the PC alone for a moment. Sure, you could use an ordinary, pretty screensaver--but you can also go for something educational like Wikipedia Screensaver. This simple screensaver displays a random Wikipedia page on your screen, and switches to a new page after some time has passed (30 seconds by default, but you can change the interval). This way, if you happen to be eating or talking on the phone while in front of the computer, you might pick up interesting new tidbits of information that you would not have encountered otherwise.
Maybe you want a screensaver that promotes science and human knowledge in general. That's what BOINC is for. The Berkeley Open Infrastructure for Network Computing is a utility that turns your computer into a node in a giant, distributed supercomputer. Simply install BOINC and select a science project to which you'd like to donate your idle computer time, and BOINC will download units of work and crunch away while you're not using the computer. BOINC-powered projects vary from epidemiology research and genetic linkage analysis to cryptography, mathematics, and quantum computing research. BOINC's screensaver component shows how the work is progressing while you're gone, but it isn't essential: If you use a different screensaver, BOINC will still run in the background.
Another great way to donate your idle processor cycles is to participate in Folding@Home. Much like BOINC, this is a large-scale distributed-computing project. While BOINC is a general-purpose platform that supports many different projects, Folding@Home is a single project that researches protein folding--a phenomenon linked to degenerative diseases such as Alzheimer's. By installing Folding@Home, you will contribute your idle computer time to the project's medical research.
Perhaps you're interested in economic theory and social experiments instead. In that case, you might like Bitcoin, an innovative social experiment in virtual currency. Each client acts as a node in a large peer-to-peer network, and the whole economic system runs without a central issuing body. Your computer can run the Bitcoin client and help "move" Bitcoins between parties making and receiving payments, and even produce a few new Bitcoins while it is idle (until a finite number of Bitcoins is reached). Although Bitcoin is controversial--and it's certainly not as solid as a bank account--it can be used for legitimate purposes, and dozens of online businesses accept Bitcoin.
As nice as contributing to the common good is, wouldn't it be great if your PC used some idle time for maintenance that you'd rather not do yourself? To offload your backup chores, try CrashPlan. This fantastic backup client can help with both on-site and off-site backup, and it's smart enough to boost upload rates and CPU utilization when you're not using the computer, making backups that much faster. When you come back, CrashPlan can dial down its settings and continue backing up in the background while consuming far less resources, so you don't even notice that it's running.
Then again, you might just want your computer to gradually shut down once you're done using it. For this purpose, consider System Silencer, Shutdown Timer, or TimeComX Basic (also available in a more full-featured, $14 Pro version). Each of these great downloads lets you mute the sound, turn off the screen, lock the workstation, or perform any other operation once you leave the computer alone for a given amount of time. Shutdown Timer and TimeComX can also execute operations once network or CPU utilization crosses a threshold that you define.
Naturally, you wouldn't want to install all of these free applications at the same time--combined, they may conflict and do more damage than good. But by selecting just one or two, you can rest assured knowing that your computer is working hard for you (or for the benefit of humanity) even while you're out enjoying the weather.