Remark is licensed under the GNU Lesser GPL, which makes using it quite free. However, Remark uses some third-party libraries whose licenses have to be taken into account also.
The Python Markdown and Pygments libraries are licensed under the BSD license, which is very allowing. These libraries are firmly integrated into Remark and therefore have essential roles in Remark. The other libraries are optional as follows.
The AsciiMathML javascript library is referred to in an html page if and only if one uses the math mode in the Remark source of that page.
The AsciiMathML javascript library is copied to the output directory if and only if some generated html page refers to it.
The Highslide javascript library is referred to in an html page if and only if one invokes the Gallery macro to generate that page.
The Highslide javascript library is copied to the output directory if and only if some generated html page refers to it.
The Python Imaging Library is used by the Gallery macro to create thumbnails automatically.
Remark is free for use in commercial products for the most part. The only exception is the use of Gallery macro which depends on Python Imaging Library and the Highslide library. To use the Gallery macro in commercial products, you need to obtain the commercial licenses for those products.