There is a feature for spellchecking already incorporated into this forum software. However, it's disabled because it relies on the services of a 3rd party. This 3rd party is changing the way in which they operate and will probably start charging to use their services. I will look into other options, but I don't think that I'll find anything.
There are two things that I'll also point out:
1) You can edit your own post if you notice that you misspelled something.
2) I doubt anyone really cares if you mistype a word or two.
3) The next giveaway will be a Webster's Dictionary. j/k