MacTerm — 

Powerful replacement for macOS Terminal, supporting 24-bit color, standard graphics protocols and iTerm2 image sequences and color schemes.  Written by Kevin Grant.

Want to donate a couple bucks to this project?

Download Version 4.1 (stable)

 — 32-bit for macOS / OS X 10.10+, ~4 MB

Version 5.0 alpha (64-bit Cocoa) currently in development!

Currently only available by building from GitHub.

To run on OS X 10.3.9+, download the older 4.0.0 release.

See also the original telnet client for Mac Classic.