After much tribulation, SpellChecker2 is now compatible with BC.
SpellChecker2 is actually a spell correction addon. It corrects by default only outgoing messages, but can correct incoming messages as well as correcting on the fly.
There are actually two readme files attached - the most important one is inside the SpellChecker2 directory.
Currently, the GUI for SpellChecker2 is not included. Sorry!
2.7 contains a toc updated and a fix for options not saving - misspelling in the toc was the cause!
2.6 contains a toc version update and a fix to enable people to use "magic characters" - %, *, -, /, +, . and so on. Lots of thanks to Bhaerau for testing! Also added undocumented /sc addraw command, only use if you wish to do raw text correction. Note that SC2 will now "escape" your strings for you, so there's no need to do so yourself anymore. Old escaped strings should work fine.
2.5 contains a mini-fix (name of a function was wrong - that's what I get for not testing fully) and a update to the addon API
2.4 contains just a minor .toc version update and makes it easier for addon authors to keep SpellChecker2 from scrambling their messages.
The 2.3 version has support for secure hooking, on-the-fly correction (/sc onthefly to toggle).
It should thus no longer cause issues with /cast or other commands. Do note that due to a limitation in Blizzard code (local SecureCmdList... GRR!) if the secure commands change, you will need to update SpellChecker2 to a newer version.