With AbiWord, you have everything you need to write a small letter, to an entire book. For more information about Abiword visit http://www.abiword.org
SkyPad is an integrated, tab-based text editor with support for synatx highlighting.
SkyOS has an integrated spell checking service. Every SkyOS TextView offers spell check support and the SkyOS API makes it very easy to implement spell check into your applications.