JLinkGDBServer 6.56 for Mac could be downloaded from the developer's website when we last checked. We cannot confirm if there is a free download of this app available.
Please check the Mac app with an antivirus before launch as it is downloaded from the developer's website, and we cannot ensure that it is safe. The application belongs to System Tools. The actual developer of this free software for Mac is SEGGER Microcontroller GmbH.
From the developer:
J-Link GDB Server is a remote server for the GDB. The application allows you to use J-Link with GDB or any toolchain that uses GDB as a debugging interface, such as Yagarto and Sourcery G++. The GDB and GDB Server communicate via a TCP/IP connection, using the standard GDB remote serial protocol.
You may want to check out more software for Mac, such as RAGE SERank or tn5250, which might be related to JLinkGDBServer.