This version of SmartGo for Mac is available as a free download. Please enjoy and use it as is, no more updates are expected. You can read more about it in this blog post.
An all-new version of SmartGo for iPhone and iPad is in the works, and the plan is to later bring that same app to the Mac. No ETA yet.
Many thanks to GoGoD and goproblems.com for letting me make the app free while keeping their game and problem collection in the app. Please support them directly at gogodonline.co.uk and goproblems.com.
Note that Go Books for Mac is another free app for the Mac. Of course it lets you read books about Go, but it's also very useful for converting SGF to diagrams.
State of the App
The app is doing a lot of things reasonably well, e.g. replaying and annotating games, joseki and fuseki matching, finding and replaying pro games, and solving problems. Other features like playing against GTP engines are working but buggy. And some key features are simply missing: editing game info, preferences, find, and problem statistics.