From the announcement blog post:
Instacast for Mac takes everything that was great about the iOS version and transfers the experience to your Mac. This means that you can expect to manage your podcast collection with ease, enjoy hassle-free playback, quickly download your favourite episodes, interact with your podcasts and synchronise your entire library with Instacast Cloud. Moreover, Instacast for Mac also has a number of unique enhancements not yet found in the iOS version. For example, you are able to easily search your entire library for specific keywords, use the Up Next playback queue to quickly manage playback order, access a large amount of storage for downloading episodes and financially support shows via Flattr.
I've been using the beta and have bee loving finally having a great podcast playing app on my Mac.
It's on sale at $14.99 until the end of May and then goes up to it's regular price of $19.99.
Screenshots of Instacast for Mac beta permalink