Searching around the net, I've realised that there is very little decent free Bible study software for the Mac. There are several commercial packages such as QuickVerse ($99) and Zondervan ($149.99) but they don't come cheap. However, thankfully for Bible scholars, there are a handful of open-source and free Bible applications and widgets that mean you can use your Mac as a tool to aid religious learning.
Accordance Although not strictly free, it only shuts-down every 60 minutes and you can restart it again immediately. Accordance is definitely the best looking and most intuitive "free" Bible study software I've seen on the Mac. Accordance is aimed at all levels of study and if you do want to upgrade, the starter package is just $49 (although the most expensive is a staggering $3000!).
MacSword This is a free & open-source application for the research and study of the bible on the Mac. You can read and browse many different bible translations in different languages and also read devotionals, commentaries, dictionaries and lexicons and more covering over 200 texts which can be downloaded from the Sword Project website.
Bible Desktop Another free and open-source project Bible Desktop runs across all platforms and relies on the JSword project for texts ranging from Bible commentaries, dictionaries and daily devotionals to more general books and hymns. The interface is pretty basic compared to something like Accordance and I had problems retrieving the books.
Logos Bible Widget Developers Logos are dedicated to Bible study software but Bible Widget is their only free offering. Bible Widget allows you to look-up any Bible verse on your Mac instantly simply by typing or pasting any scripture reference into it instantly revealing the entire verse. You also have the option of changing the Bible used from the English Standard Edition to the King James Edition.
podBible Marketed by the developer as "Put some God in your Pod" podBible is a free application that allows you to do something that wouldn't normally be possible on an iPod - put the entire text of the Bible on it. podBible gets around the text limit size of most iPods by using the Notes section of your iPod, which can hold a number of text files that support a limited amount of markup similar to HTML.
These are some of the few free bible software options that I've tried and tested on the Mac but if you've got any other suggestions, let us know!