tkSpeller is a tiny utility that sits in the corner of your screen and does nothing until you activate it. If tkSpeller is raised (selected, clicked, 'Alt-Tab'-ed into) while your clipboard contains an alpha string under 20 characters in length (a word), that string will be spell-checked. If it is misspelled, suggestions appear in the tkSpeller window. If you click one of the suggestions, that word replaces what you had in your clipboard.
The app can also be used "manually" by typing a word into the entry box along the top and clicking the check button.
tkSpeller is nothing more than a tiny wrapper around iSpell. It's written in Tcl/Tk, so you will require an appropriate interpreter to use it. A valid installation of iSpell or aSpell (preferred) is also required.
A future release will incorporate the necessary libraries and dictionaries into a stand-alone binary.