Sketch and Acorn are both well regarded Mac apps for vector graphics and image editing respectively. You can think of Sketch as an alternative to Adobe Illustrator and Acorn as an alternative to Photoshop.
Sketch 2 is the app you need to jump on as it is only reduced for around the next 24 hours (until 11pm GMT0 on May 8th). It’s 50% off, making it an appealing £17.49.
Acorn meanwhile is on upgrade offer throughout May to celebrate the new release of version 4. It is currently £20.99. I’m not sure how much it usually is – around £50 I think. It’s worth noting however that Pixelmator – a similarly featured competitor – has a regular selling price of only £10.49.