See the Colemak Mod-DH Project Home Page for information on this project.
The fastest way to try out Colemak-DH on Windows is to use the AutoHotKey scripts. See the 
autohotkey folder for downloads.
A comprehensive Colemak-DH implementation for Windows (plus many extra features) is available in DreymaR's Big Bag, EPKL edition.
There are files for Microsoft Keyboard Layout Creator (MSKLC), together with the generated installers. See the KLC folder for more information and downloads.
There is a project implementing EurKEY Colemak-DH offering Microsoft KLC files.
Support for Colemak-DH exists in recent versions xkeyboard-config (at least as of 2.34).
Usage examples:
setxkbmap us -variant colemak_dh
setxkbmap uk -variant colemak_dh_iso
A comprehensive Colemak-DH implementation for Linux (plus many extra features) is available in DreymaR's Big Bag, XKB edition
To quickly try out Colemak-DH, there are mapping files for xmodmap available in the xmodmap folder download area. You may need to customize these for your own language/region. Keymap files for the Linux console are provided by the kbd project since v2.6.2, which is included with most Linux distributions.
Alternatively, keymap files can be generated yourself by running generate script in generate-linux-keymaps.
There is a project implementing EurKEY Colemak-DH offering Linux XKB mapping files.
Colemak-DH mappings for macOS have been contributed in the macOS folder
There are Colemak-DH configurations for the KMonad program. This application allows manipulation of the raw input from the keyboard device, allowing arbitrary and advanced remapping in a cross-platform friendly way. See the KMonad folder for configuration files.
An Android Application Package (APK), with source files, is available, allowing you to type Colemak-DH on a physical keyboard connected to your Android device. See the android section for detailed instructions.
N.B. Colemak-DH is designed for touch-typing on a physical keyboard and may not be optimal for phone-based software keyboards. Nonetheless, some software keyboard apps now support Colemak-DH:
FlorisBoard - An open source soft-keyboard project (source code)