I'm working on something similar for Android but focused on note taking and diagramming instead of drawing. I think of it as a kind of handwritten wiki. I allow placing of links in the document that jump to other parts of the document. It is still very much a work in progress and my lines don't look anywhere near as good as the ones in Sketchology.
Not related to finance, but for people who enjoy Ledger and need a calendar application, there is remind[1] which works a lot like Ledger. I just have remind run from my bashrc to print out my reminders at the top of every new terminal. It works great for me.
Edit:
Looking at it again, some of the programming related symbol keys are in slightly strange positions and would require some relearning. Plus the right shift is tiny.
I'm guessing there is a lot of data that never gets sent to earth. Do they send thumbnails of the images to determine what is interesting? Is there a software tool available that creates a thumbnail and then creates a copy of the original image that is dependent on the thumbnail to be recreated. If you can't tell I wasn't really sure how to word that last sentence. Basically, less data would be required to transmit because you are only sending the data required to reconstitute the real image. Depending on the size of the thumbnail this might result in a negligible difference.
For example, a very naive implementation might create a thumbnail from every pixel where x or y is odd and then when/if you want the original image you can get the data required to put the image back together (it would be a similar sized thumbnail but with the even pixels) For this naive approach the thumbnail would likely be much larger than you want and would not help at all :)
As a Wash U student, my mind was blown to see that this is right on the Loop, rather than somewhere in San Francisco. Good sign for the STL developer community.
I'm working on something similar for Android but focused on note taking and diagramming instead of drawing. I think of it as a kind of handwritten wiki. I allow placing of links in the document that jump to other parts of the document. It is still very much a work in progress and my lines don't look anywhere near as good as the ones in Sketchology.