I work for SkyDemon (European planning and navigation app), and while we have had basic FAA charting data since we started we haven't really taken any significant steps to push into America due to Foreflight's dominance.
However, in the last few weeks we have been reviewing this, and with the kind help of a couple of guys here we have been developing our vector chart to be a bit more pleasing for the US, as well as integrating some additional US documents and data.
I anticipate that a new beta version with these updates will be coming early next week, and it would be really great if I could find a few more curious US pilots to give it a try and let us know their thoughts; ideally they would be familiar with Florida, Georgia, South Carolina and North Carolina, since those are the states we have focused on for the initial data population. We mainly develop for VFR pilot needs, but there are some IFR supporting functions too.
If this sounds interesting, feel free to drop me a PM and I will give some details about getting set up with the free trial once the beta is available.