If you’re looking for Gaelic software itself, check out one of my other sites called iGàidhlig where I collate information, links and so on about Gaelic software, where to get it and how to get it to do what it should do.
That aside, you might find l10n for Humans useful if you’d like to translate/localize something into your language but are not sure about how to start. It’s a bit basic, has more gaps than content and is mostly a scratchpad for myself but I’ve heard from a couple of folk that they thought it handy. I’ll keep adding to it if I find the time to digitize my paper notes.
One thing I can warmly recommend at this stage which might come in handy if you’re thinking of a spellchecker is Unix for Poets, an introduction to all sorts of interesting ways in which you can manipulate language data on a Unix system.