Lakeside Software's SysTrack and SysLock can help to lock out applications, as well as control the websites your users are allowed to visit; all without impacting system performance.
SysTrack tracks websites/pages visited by users and generate alerts, actions (shut down the browser) & notifications if necessary. SysTrack can also audit which applications are being used, and with SysLock shut down unauthorized application usage automatically.
Examples of apps you may not want running in your environment could include virus's, instant messenger, games, resource intensive apps, or sites like kazza.com and weatherbug.com that consume large amounts of resources.
Good luck!
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