RecipeBook (1.10.2d, 10-April-06)
RecipeBook is a mod that allows you to browse tradeskill recipes with one alt and see whether your other alts know it.

Installation: Unzip into the World of Warcraft/Interface/AddOns directory.

For example:
I have character BetsyRoss, who is a tailor by nature. She knows Pattern: American Flag, but for some reason, I can never remember this when UncleScrooge goes to the auction house to buy patterns.
* Previously, I would have to keep a written or mental list of BetsyRoss's known patterns so that UncleScrooge didn't buy her a second copy of Pattern: American Flag on accident.
* Now, with RecipeBook, UncleScrooge can mouse over Pattern: American Flag and see 'Already known by: BetsyRoss' right there on the tooltip - or, if he chooses, in a special chat tab just for RecipeBook information.

It's fun! It's helpful! It's easy to use! It's also still in development, so there are a few known issues and some miscellaneous housework to be done.

RecipeBook loads defaulted to on, tooltip output, not parsing the current alt, same faction, showing known/learn/future recipes. Banked data loads defaulted to off.
Usage: /recipebook or /rb
General:
/rb help : Displays a help message
/rb on|off : Turns RecipeBook's data display on or off. It will continue to update alts' tradeskills when the tradeskill frames are opened, so you have the best list possible.
/rb self on|off : Enables/disables parsing of the current character. May be a little redundant in tooltips, helpful in chatframe output. Defaults to OFF.
/rb config : Opens the graphical config window.
/rb output tooltip|chatframe on|off : Turns on and off the tooltip and chatframe display. 'Tooltip' adds a line to the game tooltip if and only if one of your alts knows this pattern. 'Chatframe' outputs to the 'Recipe Book' chat tab whether or not an alt knows a pattern.
/rb skill : Use /rb skill to open a window with a list of every recipe your alt knows in a given tradeskill. So, just in case UncleScrooge were curious, he could type '/rb skill betsyross tailoring' and find out every tailoring recipe BetsyRoss knew as of the most recent update.
/rb reset : Resets a given tradeskill the current character knows. Optionally, resets all tradeskills the current character knows. Useful for unlearning tradeskills.
/rb clear : Clears all RecipeBook data for a particular character.
/rb specials : Scans for tradeskill specializations known.

Sharing:
/rb send : Sends your RecipeBook data for a given tradeskill to another player. Use 'all' as your tradeskill to send all tradeskills you know.
/rb receive : For each subset of people (friends, guildmates who are not on your flist, everyone else), determine whether you will automatically accept RecipeBook shares, automatically decline, or ask to be prompted.

Friend: use /recipebook friend or /rb friend with the following options (i.e. /rb friend on)
/rb friend on|off : Turns RecipeBook friends' data display on and off

Display: use /rb for your alts' data; use /rb friend for your friends' data (i.e. /rb known off turns off display of your alts' known recipes; /rb friend known off turns off display of your friends' known recipes)
known on|off : Show/Hide characters who already know a given recipe
learn on|off : Show/Hide characters who can currently learn a given recipe
future on|off : Show/Hide characters who need only skillups to learn a given recipe (if the recipe requires a specialization, the character must have the specialization).
faction same|opposite|both : Show data for charactes of a particular faction, or both factions

BETA/In Progress:
/rb skill all : Show all of your characters (not shared) with a given tradeskill. This outputs to the RecipeBook chat tab only, not to a window.
/rb skill all : Show all known tradeskills for a certain character. This outputs to the RecipeBook chat tab only, not to a window.
/rb banked on|off : Show/Hide banked item information in a tooltip (DEFAULTS TO OFF)
/rb bank : Use /rb bank + shift-clicking a recipe (as if you were linking to the chat window) to mark that recipe as banked.
/rb unbank : Removes a recipe from the banked list. You may also type the recipe's *exact* name in, enclosed in square brackets, to add/remove it (i.e. /rb bank [Formula: Enchant Gloves - Greater Agility]).
/rb banklist : Displays your banked items.
/rb autobank on|off : Automatically tracks recipes in your bank. Updates when bank window is opened or closed. (DEFAULTS TO OFF)
/rb autobag on|off : Automatically tracks recipes in your bags. Updates with autobank (if autobank is on) and on logout. (DEFAULTS TO OFF)

Known issues:
* RecipeBook only updates its recipe list when your tradeskill window is open. So, if BetsyRoss just learned Pattern: Giant American Flag, she'll have to open her Tailoring window before RecipeBook (or UncleScrooge) knows about it.
* Depending on what other mods you're running (I've noticed this with Auctioneer and Lootlink), the tooltip line may come in a variety of interesting places. Most commonly, either at the very end of the tooltip or right underneath the default Blizzard info. Wherever it decides to go, it's usually consistent within a particular frame - i.e. Auction tooltips will be in one place most of the time. I wish I could fix this for you, but I'm still working on it.
* Old versions of Averice's WIM will capture RecipeBook share data and parse it as a whisper. Still works, just spammy. :)

Housekeeping:
* Definitely up next: GUI output for /rb banklist.
* Things to add: Integration with Lootlink/KC_Items for /rb skill enhancement.
* Hopes for next phase: Updating your recipe list when you learn items (in progress). Colour-coding customization.

Special thanks to:
Curse Gaming's Pentarion and Ghandi, for some hard work helping me debug the German client version. Particularly to Pentarion for ongoing translation work.