Acorn 4.5.9 2017.
Fixed Stuff
Acorn 4.5.8 November 21, 2016.
Fixed Stuff
Acorn 4.5.7 January, 2016.
Fixed Stuff
Acorn 4.5.6 September 29, 2015.
Fixed Stuff
Acorn 4.5.5 June 15, 2015.
New Stuff Fixed Stuff

Acorn 4.5.4 January 30th, 2015.
Fixed Stuff

Acorn 4.5.3 January 7th, 2015.
Changed Stuff Fixed Stuff

Acorn 4.5.2 November 18, 2014.
New Stuff Fixed Stuff

Acorn 4.5.1 September 3rd, 2014.
Minor New Stuff Fixed Stuff

Experimental Stuff
Acorn 4.5 July 28th, 2014.
Acorn 4.4 May 26th, 2014.
Acorn 4.3 January 24th, 2014.
Acorn 4.2.3 January 4th, 2014.
Acorn 4.2.2 Dec 10, 2013.
Acorn 4.2.1 Dec 8, 2013.
Acorn 4.2 Dec 6, 2013.
New Stuff:
Bug Fixes:
Acorn 4.1.2 October 25th, 2013.
Acorn 4.1.1 September 18th, 2013.
Acorn 4.1 2013.
Acorn 4.0.5 June 20th, 2013.
Acorn 4.0.4 May 21, 2013.
Acorn 4.0.3 May 7, 2013.
Acorn 4.0.2 May 2nd, 2013.
Acorn 4 May 2nd, 2013.

Tools get their own palette now.
It was getting cramped in there, so we broke out the tool icons into their own palette. In addition we updated a bunch of icons and made everything look better in general.

Layer styles and Filters sitting in a tree…
We rolled the layer styles and filters interface into a single non-modal window. This also means that filters are non destructive! You can still chain together filters like before, but now you can undo and redo your adjustments and even save them as part of your Acorn file. In addition to the filter settings being in a non modal window- you can now directly modify filter parameters right on the layer by dragging any little circles that show up when the filter window is present! (And if you'd like the previous filter window back for some reason- we're keeping it around for a little while- just hold down the option and command keys when choosing your filter from the Filters menu.)

The one exception where the filters window isn't modal (and is destructive) is when you are using a filter on a selection.

Curves Adjustments (finally!)
Acorn now has a Curves Adjustment tool, which you can get to from the Image ▸ Curves… menu. To add a new point on a curve, click on the curve and start dragging. To remove a point on a curve, drag it either left or right until it's past the location of the next point on the curve.

Vector tool improvements.

Levels tool improvements.
The Levels window got a complete rewrite, with a gamma option (to control mid-tones) as well as an option to update the histogram live.

Speed improvements.
Compositing, filter previews, and everything in general is faster. Way faster Flood Fill, Magic Wand, and Instant Alpha tools. The Render Clouds filter got a little speed bump as well.

Multiple layer selection.
The layers list now allows you to select multiple layers. This means you can re-order, delete, move, or lock a bunch of layers at once.

Other great things worth mentioning.

Stuff for Scripters: