The spell check utilities (SCU) builds off the Wintertree Sentry Spell Checker Engine (SSCE) by providing the glue code, in the form of a plugin, to access the SSCE routines in REALbasic. The price of this plugin is very expensive (500 $) but is always good to know that somewhere there is this kind of solution.
The problem with many spell checking solutions in the REALbasic market place is that they use platform specific built-in services to provide spell checking. This is fine if you want to build for only one platform or the other, but becomes a hindrance when you want to create a cross platform application that behaves exactly the same for every platform. The SSCE is a fast, professional, cross-platform spell checking engine and has many features and benefits. The SCU is supported for Mac OS X, Windows, and Linux platforms.

Looks cool, but wow, $500 is a bit steep. You can buy the MBS plugins and get access to the Cocoa spell options. Or you can do it yourself for free using the iDeclare site to learn the declares (harder). Or you can wait till Cocoa support comes out, hopefully soon, and get spell check for free, as it was one of the announced features…
Failed to mention that the Cocoa and iDeclare options are both OS X only.
I will try to create this kind of solution in one of my tutorials in future. Some concept how can this be done
And yes, Spell Check Utilities is definitively to expensive.
MagicSpeller for REALbasic is a much better option and it cost only 25 USD.
http://realbasic.tutspolis.com/plugins/magicspeller-for-realbasic/