I got a copy of the ARRL handbook (2020) edition, flipped it up to the section on D-Star and was amazed at how out of date it was. A number of links lead to pages that have been out of commission for eight or more years.

The ARRL Handbook is silent about the the Kenwood D74.  Homebrew and kits seem to be stuck in 2008.  (They're still assigning gender to robot drones... but that's another rant).  It's 2020, already, ARRL.  Rather than just complain, I'm going to add some material here so that I can offer a suggestion for the 2021 handbook.

Overview

• 2017 roundup on Dstar Info.

User Groups

• Roundtable discussions.
• General Redit discussions.

Homebrew DStar

• Multimode Digital Voice Modem (mmdvm) (Active 2019/20) and GitHub repo.
  • 2016 Hackaday article.
• 2014 project by K6JM.
• 2015 project using a RPi and Motorola radios.
• 2017 roundup on Dstar Info.
• Mid-2000s round-up of home-brew projects.

Commercial DStar

• Kenwood D74 handy talkie.
  • Official Page
  • Tips PDF
• Icom 9700
  • Official Page
• Kits
  • OpenSpot (v3)
  • DVMega : complete solution, Arduino add-on, Raspberry Pi add-on., and USB stick.
  • Sainsmart multi-mode radio
  • MMDVM
  • BlueDV (used to be BlueSpot)
    • Good overview

General pages on Digital Modes

• On hotspots (MMDVM / ZUM and OpenSpot)
• On making a homemade repeater (Digital Voice)
• Overview of DSTAR and alphabet soup. (Jan 2020)