Under the category "The Next Big Thing," file a new type of software called the personal information manager. But that is probably the only place you'll be able to file it right now, because this new software has a bit of an identity problem. So far, it's been called everything from the mundane "data base" to the esoteric "hypertext" to the whimsical "mysteryware."

Personal information managers are taking many forms, but the two to watch so far are Agenda for IBM and compatible personal computers from Lotus Development Corp. and HyperCard for the Macintosh from Apple Computer Inc.

These programs differ in format, but both are designed to help professionals get organized. Agenda is due out next spring and will cost $395, while HyperCard is free with the purchase of a Macintosh computer. It costs $49 if you already have a Mac.

Because many professionals have trouble getting organized, the idea behind PIM's is to let the computer help them. The software does this by providing a container for a variety of information pieces. The PIM works to put the pieces into readily accessible and organized packages. Those information pieces can be dates, names, telephone numbers or most any other snippet.

In Agenda, for instance, the user is encouraged to type in scraps of information. Later, the user can connect the pieces and, more important, interconnect them.

So, a single entry of John Smith of a certain city and his telephone number could later be used in a list of people at Smith and Jones Co., on a list of contacts in that city and on a list of phone numbers. And if any information on John Smith changes, altering the entry in one place in Agenda will change it in all the others.

One of the forces behind Agenda was former Lotus Chief Executive Mitch Kapor, who "was constantly stuffing bits of paper into his pocket with notes on them," said Conall Ryan, Lotus' product manager for Agenda. "He wanted to develop a package to help manage those little bits of information."

Agenda can be compared to a personal secretary, says software industry watcher Esther Dyson, president of EDventure Holdings Inc. of New York. "It would be great to have a list of hotels and a list of companies you're going to visit," Dyson said. "Then, when you decide which five companies you're going to visit, you can prepare a list of the hotels near them."

While data bases can link lists together, they are difficult to use. PIM's are "free form" and have have no rigid structure into which users must shoehorn data. Called "nonlinear writing with free user movement," Hypertext is information organized not by the traditional table-of-contents hierarchy, but by a complex series of interconnections. In a hypertext history book, the mention of the Model T is connected to the biography of Henry Ford.

So influential is hypertext that Apple named its PIM, HyperCard, after it. HyperCard is more of a development tool for a PIM that requires "stacks" of information that are interconnected with HyperCard's hypertext abilities. Activision has released two pieces of "stackware," and there are countless more on Macintosh bulletin boards.

HyperCard's distinguishing characteristic is that it interconnects images as easily as words: A HyperCard stack could replace a medical text by showing a picture of the human eye, from which a student could point to the iris on the computer screen and be transported to a written chapter about it. Pointing to the word "iris" on the screen would then bring the student to a close-up.