mupen64plus-libretro is mupen64plus + GLideN64 + libretro.

This package was previously called GLupeN64.

How is this different from parallel-n64?

mupen64plus-libretro implements multiple Graphics plugins. There are also
code modifications that make it different than standalone mupen64plus.

Mupen64Plus uses GLideN64 (a graphics plugin that is not available in
mupen64plus-libretro). The emulator code itself is identical to
standalone mupen64plus.

By choosing one graphics plugin (GLideN64), we will be able to keep the
code in line with upstream, and maintaining the code will be much simpler.

mupen64plus-libretro optionally supports using OpenGL ES 2 and OpenGL ES 3
instead of OpenGL which will require support in the libretro frontend, video
card and driver. This can be done by building mupen64plus-libretro with:
  GLES=1 ./mupen64plus-libretro.SlackBuild
or
  GLES3=1 ./mupen64plus-libretro.SlackBuild

To build the debugging symbols use:
  DEBUG=1 ./mupen64plus-libretro.SlackBuild