Serial is described as 'Full-featured serial terminal for the Mac' and is an app in the Development category. There are seven alternatives to Serial for Mac, Windows, iPhone, iPad and Linux. The best alternative is KiTTY, which is both free and Open Source. Other great apps like Serial are iTerm2 (Free, Open Source), Prompt (Paid), Zterm (Free) and CoolTerm (Free).
iTerm2 is a replacement for Terminal and the successor to iTerm. It works on Macs with macOS 10.10 or newer. iTerm2 brings the terminal into the modern age with features you never knew you always wanted.
CoolTerm is a simple serial port terminal application (no terminal emulation) that is geared towards hobbyists and professionals with a need to exchange data with hardware connected to serial ports such as servo controllers, robotic kits, GPS receivers, microcontrollers, etc.
Get Console is the first ipad and iphone serial port terminal application providing serial terminal connectivity without jailbreaking. The app store description advises it works on network devices, but offers a standard VT100 emulation.