I'm using Acquia's DevDesktop on Windows 10. For a shell, I'm using babun's zsh. Acquia provides the drush command line interface to Drupal.
The command itself seems okay:
{ drush }  » pwd                                                                                /cygdrive/c/Program Files (x86)/DevDesktop/tools/vendor/drush/drush 
{ drush }  » ./drush                                                                            /cygdrive/c/Program Files (x86)/DevDesktop/tools/vendor/drush/drush 
Execute a drush command. Run `drush help [command]` to view command-specific help.  Run `drush topic` to read even more documentation.
...
I created a symlink for it, but it doesn't work:
{ drush }  »  ls -lha /home/username/bin/drush                                                    /cygdrive/c/Program Files (x86)/DevDesktop/tools/vendor/drush/drush
lrwxrwxrwx 1 username None 73 Aug  1 23:29 /home/username/bin/drush -> '/cygdrive/c/Program Files (x86)/DevDesktop/tools/vendor/drush/drush/drush'
{ drush }  » cd ~                                                                                 /cygdrive/c/Program Files (x86)/DevDesktop/tools/vendor/drush/drush
{ ~ } master »                                                                                                                                              
{ ~ } master » drush                                                                                                                                               
Could not open input file: /home/username/bin/drush
I tried changing the permissions, and ensuring line endings are correct, as per this answer, but it still doesn't work.
{ ~ } master » chmod 775 /home/username/bin/drush   
{ ~ } master » dos2unix -F /home/username/bin/drush                                                                                                               
dos2unix: converting file /home/username/bin/drush to Unix format...
{ ~ } master » drush                                                                                                                                               
Could not open input file: /home/username/bin/drush
What am I doing wrong?