It doesn't happen very often, but I'm releasing two updates to Acorn today: 5.1 as well as 4.5.6. If you're running the direct version, you can use the Acorn ▸ Check for Updates… menu item to grab the latest version. If you're using the App Store version, you're going to have to wait a bit for Apple to review and approve it.
First up- what's new in Acorn 5.1?
Some bug fixes, as well as minor compatibility fixes for OS X 10.11 El Capitan (most of the 10.11 fixes were in Acorn 5.0.1 already). But there are also some neat new features if you'd like to script Acorn from the command line, as well as Taptic feedback when aligning things to guides or canvas edges (this is available on 10.11+).
And another slightly big thing- basic SVG support. This has been a huge request for a number of years, and I'm happy to finally have something started for you in Acorn 5.1. Acorn doesn't support all the features that SVG provides (nor should it)- but it does a pretty decent job of getting vector objects and layers out of Acorn in a scalable format that'll be around for years to come. Look for more SVG improvements in future releases of Acorn as well.
And what's new in Acorn 4.5.6?
Compatiblity with OS X 10.11 El Capitan, and other bug fixes. Acorn 4 is still a great usable app- and we'd like to keep it that way.
We've also submitted Acorn 4.5.6 to the App Store- though it's been removed from sale. I've never tried updating an app that's been removed from sale, but hopefully it'll sail right through review without any problems.