With a lot of people talking about Roll20 and Fantasy Grounds, I think if you have the rulebooks, all you need to play D&D and other RPGs with friends online is a space to share character sheets, dice rolls and manage the characters in space and TTS has all that, except a decent way to share the character sheet.

The best idea I can come with is to improve the notebook menu, like making the player choose to show his notes to everyone so it could keep color coded and still visible to everyone, and the ability to add tables, so the GM can make a template and everyone else just copies and fills their own sheet, even better, add the ability to add a background image, so the player (or GM) can create one with a blanc sheet as background, and align the tables with the sheet spaces so the sheet will look super official. Even better, the ability to create more "notebook menus" one just with character sheets, other just with tables and rules for the DM, like a screen shield.

Another option would be make a better notecard, maybe with all that I said but physically on the table. Wich would be even better I think, although having every character and sheet on an easy-to-access-always-visible-menu would be super convenient, maybe instead of editing the title and body with plain text (and BBCode!) It could be an "edit" menu.

Here is an exemple of what we have so far vs what I mean
Desktop Screenshot 2018.10.06 - Screenshot 2018.10.06 - - Copy.jpg