A fantastic font named Al Kanz Font which works everywhere, I mean everywhere: Windows 10, 8 Mac, iPhone, Android everywhere - is developed by NujoomApps. The download link for every platform is provided on site.
Definitions are a real bore... people don't understand a word from it's definition, but rather from its usage. So it would be a waste to even try to "define" Lisan ud Dawat.
From a font designer's point of view Lisan ud Dawat is the arabic script with some features of farsi incorparated in it, not all, only a few.
There are many languages which use the arabic script, and add the extra sounds and alphabets which it needs. For example, baluchi, pashto, and other afghan languages.
This seems interesting because, if someone needs support for writing Lisanud Dawat (on a computer of course), then he should look or farsi support, or any of the languages mentioned above... Any software that supports farsi could support Lisan ud Dawat too...
Or at least this is how people thought a few years back... (may be when people used windows 3.1, 95, and ME) but...
Wide spread Unicode support changed all that... it would be the same to say... Windows XP changed all that... Anyway, enough of history...
in the present scenario... Pure Unicode support is still a bit hard to come by... prior to that there were many propriety formats... and many still lurk around and make our life a bit difficult.
(ever faced a file which was arabic, and is now chinese characters?, or french chars? or even junk chars? sounds familiar doesn't it!)
Some times the problems faced raise questions like:
Q: Why should we be even use this format?
A: 'cuz its the STANDARD...
Q: Do we need to follow the standard... cuz Lisan ud Dawat doesn't have it own characterset in unicode? We could use our own format and make it the a standard!
And questions like:
What makes a Standard a Standard?
Which takes us back to our original question what is Lisan ud Dawat?... The boring question of definitions...