Types of freely redistributable software
A short intro to some of terms used to classify the types of re-distributable software you will find on the net.
Public domain software
Software that you may use as you wish since all rights to it have been explicitly vacated by the original author, sometimes comes with source and sometimes not, but copyrights and copyright law does not apply since it has been deliberately placed in the public domain.
This software is very similar to open source, but this refers to the licenses approved by the Free Software Foundation. From the Free Software Foundation comes the statement “Free as in Speech” or “Free as in Beer” to differentiate the meaning of "Free Software" against "Free of Charge Software".
The only valid "Free Software" licenses are the one listed by the Free Software Foundation . Many of this license also fall in the category of Open Source.
Software that you can distribute and in most cases use as you wish but is copyrighted by the owner who retains all rights to the software even if he allows free and unlimited re-distribution of the package as is, the software can be supplied in source or binary form although the latter is much more common. The term came into being in the 80s as a way to distinguish PD and other free software from Demoware and Shareware that while re-distributable, ultimately required payment for continued use. Lately there have been attempts to hijack the term for "Free software" but that is an ambiguous term used by advocates of certain restricted distribution and use open source licenses, but this should be discouraged since the term "Freeware" has a long history and attempts to shape the meaning to a political ideal will only cause confusion.
A concept that dates back to the microcomputer user clubs of the 1970s and 80s but really took off as BBS got popular. Shareware is software that is commercial in nature but is marketed by allowing people to share copies of the software, sometimes with restrictions. The software can be fully functional or have some functions restricted to encourage people to "register" the product (buy a license in other words) but it varies from package to package and so do licensing terms and usage restrictions.
Freely re-distributable software that has bee limited in some way to make it usable as marketing tool but of limited or no value as an end product. The limitation can be time, specific functionality or generic functionality such as the ability to save your work. There is sometimes a bit of a grey area between Demos and Shareware. Note that in home computer parlance a demo can also be a type of graphic and sound program intended to show off the capabilities of the computer system, OS's or programmer rather than to have an inherent function.
Functionally limited versions
Freely distributable software that has limitations in specific functionality only but no time or generic functionality limitations. This is fully functional software that is intended to give you an insight into how the full software package works and entice you to fork out for the full version that has more advanced or sought after features, but you are also free to continue to use it as is. Commonly known as Lite or light versions, they are often also called "essentials", "express", the term "limited edition" is seldom used since it can be misunderstood, but its acronym in the form of LE is common. These packages are sometimes classified as demos. Craplets is slang for software that is functionally limited to such a degree that is at best a demonstration software even though the maker maintains it is usable as is for some function.
A type of software package that is freely re-distributable but in order to get a full license for its use you are expected to send the author a postcard with your contact details. Terms and conditions differ, sometimes you are expected to send a postcard if you find software is useful in any way while other authors will email you either a "full" version of their package or the source code to it in response to a registration. Many minor variants of this theme exist such as "E-Mail Ware" and so on, so forth.
Software that is publicly available in source code form as well as or instead of binary/executable format. Note that as software is always legally considered intellectual property and therefore copyrighted automatically unless it has specifically been placed in the public domain, therefore there are bound to be some restrictions on how you can use the source code whatever its source and it is important that you read the licence or readme files that come with the source. See our partial list of licenses.
The only valid "Open Source" license are the ones listed by the Open Source Initiative organization .
Open source history
During the early years of informatics there was little or no need for open source since all software was entered in assembly or binary form and in the latter case therefore no "source" per se and there was a limited amount of transferability since storage mediums were primarily ticker tape (a la Telex machines) and a limited amount of machines to duplicate to. After the introduction of programming languages, the rise in use of storage mediums that could be easily duplicated such as magnetic tapes and punched cards and in general the mushrooming of computing machinery, we ended up with a situation that was almost the opposite of what it was today. Commercial software vendors always included source code for their products so that companies could adjust it their machinery and other software and companies in general treated software more as a service than an intellectual property, free software on the other hand was generally either not made available at all except by signing a license agreement or only available in binary format. This was especially problematic with USA universities that generated lots of code but were unwilling to share partly due to pressures from their legal departments that saw software as IP and wanted to treat it as a revenue stream like other IP that the schools generated.
This lead IBM to instigate the first open source drive in 1957 and indeed to coin the term "open source", in the 60s DEC lead a similar drive and organised a number of user groups to encourage the sharing of software, this was in particular successful in regards to their LINC workstation and VAX minicomputers and the large library of freely available software become one of main selling points of DEC hardware. IBM put their money where their mouth is by offering all of their software in source format, however this started to backfire when manufacturers of IBM compatible hardware started to sell their products with modified versions of IBM's software, Amdahl being a notable example of this practice. This meant that by the late 70s IBM had started to copyright all of their software and in the 80s most of their software had become closed source.
Note that at the time the law in the USA required you to place a copyright notice on the mechanical reproduction of your work, register the work with the USPTO or both to get copyright protection, this made the placing of the work into the public domain easy as the companies simply neglected marking their source printouts or tapes with a copyright notice but placed such a notice in their documentation. This made it abundantly clear that the software was in the public domain while the documentation was not.