Pike is distributed not only under the GNU GPL license, but also under the GNU LGPL and the MPL licenses. This means that you are free to use and redistribute Pike under the conditions imposed by either license, or all, for that matter. You may thus choose to build applications of your own that heavily borrows code from Pike and license it under GNU GPL, or, if you prefer, use the code under the terms listed in the MPL license. Your contributions to Pike (be it code, documentation or otherwise) are considered donations to the Pike community in general and IDA in particular, in the legal sense. Note that your local version of the code is still your own, so that you might reuse it in other projects and for other purposes, without risking that IDA take legal actions against you for doing so. Providing contributions means that you agree with these terms.