Both the Microsoft Typography and Adobe Opentype web pages contain official specifications as well as extensive listings of all currently defined features. Most of them come down to "this feature should be implemented as a Single Lookup, and that as a Contextual one" -- not much of programming required.

Combining the few available commands can make things interesting; take, for example, Tal Leming's Fraction Fever 2. There are also a couple of threads in the Build section that discuss writing out arbitrary numbers in Roman form.

Anything particular you are looking for?

can i get a system timestamp? Is there a random function? What laguage is it closest related to syntax wise?

OT feature code is not a programming language in the usual sense. There are no functions for system info, there is no random function, there are no functions period.

I find it's easiest to think of it as a formalized kind of search and replace language, something like GREP or regular expressions.

http://www.microsoft.com/typography/otspec/features_ae.htm

It would be nice if layout apps supported the random feature.

At the moment, complex pseudo-random coding has to be put into the font, included in a feature such as “calt”. Most annoyingly, it doesn’t work (in InDesign) when tracking exceeds +20.

Ideally, I would like to be able to create several glyphs all named “a.rand” in a font, and put a simple instruction in the “rand” feature: sub a' by a.rand; —and then the layout app would cycle through the alternates. Or some such thing.

There are 2 OReilly books, Unicode Explained and Fonts and Encodings also.

There is an operator called "rand" in the CFF specifications -- but I doubt it is supported by all (or some) type engines.

I can't imagine anyway how that would work in an interactive way, such as when typing in text. Would you see the glyphs on screen squirm and wiggle as you are typing? How about system redrawing -- zooming in and out would also cause your glyphs to change!

I suppose the same goes for attempting to support the OTF feature "rand", as it may display these same side effects.

my idea was to have three our four versions of the same glyph and simply have the engine chose a random one on every corresponding keypress. So it wouldnt really be controllable by the user at all. Or, to hide an easter egg in the font, for example to have it morph into something similar to comic sans every april first for the entire day. I am a playful one.

http://ilovetypography.com/2011/04/01/engaging-contextuality/

can you look back two glyphs?
sub a b c’ by c.alt ;

You can't check the time or date, except for the aprf table that only works tomorrow.

Apparently some sort of pseudo random glyph substitution is possible, though I don't quite understand it.

http://typophile.com/node/19625