MacTerm — 

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

Download Version 4.1 (stable)

 — 32-bit for macOS / OS X 10.10 - 10.14, ~4 MB

Version 5.0 alpha (64-bit Cocoa macOS 10.15+) 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.