After doing a quick research:
Screpy looks like it has a nice Tasks system, which is somewhat similar to the Next SEO Goals system. However, Next SEO Goals from Squirrly covers a broader range of aspects. (you can learn more about this feature from Squirrly here).
Screpy also seems to focus most on monitoring.
Squirrly also covers this with features such as the SEO Audit Suite, rank tracking, and more. But it also helps to actively improve your rankings with features such as Focus Pages, SEO Live Assistant, keyword research tool, Bulk SEO, and much more.