Currently we don't have spell checking. There is spell checking support in wx.TextCtrl but it's not consistent across platforms, so we aren't bothering with it right now.

The two major OSS options are GNU Aspell (LGPL) and Hunspell (LGPL or MPL).

Possible approaches:

1) System-based -- use system built-spell checking when available, and use Aspell or Hunspell on Linux and/or as a fallback.

2) Consistent -- use Aspell or Hunspell everywhere.

It should be toggleable in the settings or in the toolbar/menus somewhere.

It should probably default to "off" in normal/writing mode. If we implement the editing mode (bug 1400), it should probably default to "on" in that mode. But users should have the ability to toggle it on/off in either mode separately.