A program often found on Macintosh (Classic) computers in elementary schools, At Ease provides administrators with a means of sharply restricting access to the computer. On boot, a file called At Ease Startup is read, and a menu of choices (usually with large, friendly buttons with icons on them) is presented to the user. Additional tabs and programs may be added by administrators. To enter administration mode, a password is required; if At Ease terminates for whatever reason, it is immediately restarted.
Some versions of At Ease suffered from a vulnerability: if a user saved a file from any application as "At Ease Startup" in the appropriate folder, At Ease would crap out on startup and the Finder would display instead -- giving malcontents free reign over the whole system. It was also possible to reboot with extensions off (by holding down the SHIFT key on boot) to go straight into the finder.
Fortunately, the ability to add Multiple Users in Mac OS 9 and Mac OS X enabled administrators to simply restrict permissions on files. Macintosh Manager also helped to make At Ease obsolete, and so At Ease is rarely seen on Macs today.
According to Low End Mac, if you come across a computer with At Ease installed, the easiest way to get rid of it is to reinstall Mac OS. Because At Ease is integrated into the OS, trying to remove it separately can cause some serious problems.