There is no single established software or service called "RTNK zip." Depending on what you are looking for, you may be referring to one of two very different things: a regional news application or professional engineering software.
Only download software from official domains like rtnk.me for news or openrtk.org / rtklib.com for engineering tools. Download RTNK zip
This is an open-source program for precise GNSS positioning. You can download the latest package, such as rtklib_2.4.3.zip , from the official RTKLIB website or GitHub repository . There is no single established software or service