By placing a file in an anonymous FTP archive, the author allows free access to it by individuals all over the world. In general, however, such files are not totally free of restrictions. This column is a brief look at the kinds of restrictions you may encounter. (Please bear in mind that the author is not a lawyer, etc.)
Even if a file contains no copyright notice, it is still copyrighted by default in most countries. In countries that honor the Berne Convention (e.g, the USA), an author has an implicit copyright on his or her work, unless it is specifically disavowed. If you don't see a notice such as "This software is in the Public Domain", you should assume that a copyright exists. (By placing a work in the public domain, the author explicitly disclaims all copyrights and related restrictions.)
You might think that no sensible person would rely on such protection, but many institutions and individuals actually do so all the time. For example, many dissertations and other papers are available for FTP, but are not available for redistribution by organizations like mine. A few software packages also have such "hidden" restrictions.
Fortunately, these restrictions are seldom relevant to individuals and organizations that merely wish to use the files. In fact, most explicit copyright notices allow just about any kind of use. Redistribution is another matter, of course. Contact the author(s) if there is any question; careful inquiries will generally get a prompt and polite clarification. Bear in mind, however, that some authors are a bit confused: I have seen more than one notice of the form "This is software is in the public domain, and you can only do X,Y, and Z with it."
Among more formal software license agreements, two variants seem to dominate. University software tends to contain notices that allow the software to be used for any purpose, as long as the copyright notice is maintained. The Free Software Foundation's General Public License allows any kind of use, but requires redistributors to follow certain rules, as discussed below.
Even with formal language, however, the restrictions can be unclear. gnu.misc.discuss, a discussion group for Free Software Foundation (FSF) and GNU Project issues, is rife with claims and counter-claims about the meaning of the General Public License, despite the fact that it is a very clear and readable document. University notices can also be confusing; MIT's X Window System code includes the following text:
Permission to use, copy, modify, and distribute this document for any purpose and without fee is hereby granted, provided that the above copyright notice and this permission notice appear in all copies, and that the name of MIT not be used in advertising or publicity pertaining to this document without specific, written prior permission. MIT makes no representations about the suitability of this document for any purpose. It is provided "as is" without express or implied warranty.
Very similar notices can be found in software from a number of universities. It all seems pretty clear, except for the phrase "without fee" Does that mean that the university won't charge a fee, or that I cannot do so. Believe it or not, I got differing interpretations on this from different institutions (sigh).
Some freeware and shareware packages are distributed only in binary form. The attached licenses generally allow redistribution, but may limit the amount that can be charged for copies. Consequently, neither of these are "Free Software" in the FSF sense. Finally, the proprietary binary files that show up on some FTP archives are not free in any sense except the financial one. They generally aren't full-featured code, and are only placed on the archives as a cheap form of advertising. The owners generally ask users not to decompile these programs or otherwise subject them to analysis. Just try them out, I guess, and hope they don't blow up your machine.
The word "free" means different things to different folks. Many people assume that free software is analagous to free beer; no charge is levied for its use. The FSF uses word to mean freedom: one should be free to read, modify, and redistribute software. Both GNU and X Window code (as received from MIT) are free under this definition. Redistributors and repackagers of X may change the rules, however.
To ensure that their software remains free, FSF imposes restrictions, embodied in their General Public Licenses. You can build and sell binaries based on FSF software, but you must be willing to provide complete source code, and you can't restrict the recipient from, for example, giving it away. Finally, the licenses generally prohibit the receiver from adding or removing restrictions.
Proprietary software vendors may use different definitions. Univel recently allowed my firm to redistribute, under license, a set of UnixWare include and static library files. These files are free to my company and its customers, in an economic sense, but they are not free in the FSF's terms. They cannot be redistributed, and can only be used under Univel's license. I included them because they made the other 99% of the distribution usable, but it wasn't a clean or easy call.
A recent advertisement strays even further from the FSF's definition. The two-page ad proclaims that "Our Subs Have Surfaced with Free Software" Further reading reveals that the software in question is actually proprietary software, bundled in with the vendor's hardware. I hope the firm in question cancels or modifies the ad campaign soon. It is well on the way to confusing a great many folks about the term "Free Software" as well as seriously irritating the FSF and its many friends.
In an effort to avoid such confusion, Cygnus Support has trademarked the term "Sourceware". Sourceware is software which is available in source form and which provides both the right to freely redistribute it and a source of reliable commercial support. Thus, arbitrary public domain software may be freeware, but if it is backed by Cygnus (or another support provider licensed by Cygnus), it can be branded with the Sourceware label. Cygnus has adopted the GNU C and C++ development tools as part of their initial Sourceware offerings. Proprietary source-licensed code is clearly not Sourceware -- it lacks the property of free redistribution (and often any reasonable sort of commercial support).
I have mixed feelings about the new terminology. The new name avoids the problems associated with the old one, but fails to retain the notion of freedom, and indeed only covers a small part of the freeware spectrum. If Cygnus is successful in promoting this term, the abuse of the word "free" will be reduced, and that alone will help users and free software. (I am assuming, from their track record, that Cygnus will not simply use the new trademark to stifle competition.)
In any case, roam the net freely, and enjoy what you find. The presence of hundreds of gigabytes of free (mostly in the FSF sense) material is a stunning tribute to the open-handed and cooperative spirit of the Internet. If you have something to contribute, make it available: information only grows in value through sharing.