The TextCite program is free, and is made available under an open source license, the GPL version 2, published by the Free Software Foundation (FSF). This license can be read by selecting the menu item "Help | About TextCite", and selecting the "License" tab.
Open source software is that which is distributed under a license that permits that the source code of the program be made available and open to modifications by third parties. Open source software can be sold, although in the majority of the cases, it is free of cost, as in the case of TextCite.
The GPL v.2 license implies that the source code of TextCite will be available to anyone who wants to make use of it or modify it, and the modified source code can be redistributed, provided that it is done under a license that is compatible with the GPL v.2 (e.g. under the GPL v.3). This means that it is illegal to incorporate the source code of TextCite in any program or code library that does not conform to the requires of the GPL; in particular, it is prohibited to incorporate the code of TextCite into commercials programs.
On the other hand, you are free to make as many copies of TextCite as you wish, and redistribute them to any person or group, provided that the recipient(s) is/are made aware of their rights under the GPL v.2 license, and that they have access to the source code, if they so wish.
The provision of TextCite under the GPL v.2 license does not constitute nullification or alteration of the licenses of the code libraries upon which TextCite depends (see Credits). In order to use any of these programming libraries in another program, you must follow their individual licenses, which may be different from the GPL v.2.