Dependencies:

rolldice for, uh, rolling dice
bc for calculations

Features

System-agnostic: Character sheets are stored as YAML files, and the data structure is not designed with a particular TTRPG system (ie dnd5e). You can make a template for your favorite system! This is also a bit of a downside; rpgsheet is quite usable, but you might miss some niceties that it could provide if it knew more about your specific system.
Flexible: You can define whatever tabs or windows you want for your character sheet! The template is just a starting point.
Auto-rolling: As long as your system uses dice rolls that can be represented with the standard NUMdFACES+MOD notation, you can easily define actions which will automatically be rolled.
Auto-calculation: You can define values in your character sheet which are dependent on other values. For instance, you can define a hard-coded proficiency value, and then define your shortsword attack modifier as 3+proficiency. (For DnD, you probably actually want a hard-coded strength ability score, then a STR value defined as (strength-10)/2, then define your shortsword attack as STR+proficiency.)

Unimplemented planned features

Configurable controls
Be able to have a tab with multiple rows of windows

Planned related projects

dndsheet -- rpgsheet but with a streamlined dnd5e-specific interface which, given a sheet following a particular standard, can provide an experience tailored to the system.

Installation

Install Nim and run:

nimble install rpgsheet

You can also clone this repo and then run this in the directory:

nimble install

The sheet format

Sheets are stored as YAML files. Keys are limited to alphanumeric characters, plus _, ~, and '. When displayed "nicely" in the interface, _ is converted to a space, and ~ to a hyphen.

All window names and expressions (items that go in windows) must have unique names.

Here is an extremely pared-down design so you can see the structure:

name: Character Name
class: Character Class
level: 1
tabs:
  - main:
    - stats
    - inventory
  - attacks:
    - weapons
    - spells
expressions: # items that appear in the windows
  strength:
    modifier: 15 # use `modifier` for flat values
    window: stats
  STR:
    # Modifiers can be defined in terms of
    # other diceless expressions
    modifier: (strength-10)/2 
    window: stats
  sword_attack: # we cannot have two expressions named `sword`
    dice: d20 # must be in NUMdSIDES format; no modifiers
    modifier: STR # here is where your modifier goes
    window: weapons
    # Extra information, shown at the bottom of the screen
    desc: Swing your really cool sword
  sword:
    # Note that you don't need to supply dice or modifiers
    desc: Your really cool sword
    window: inventory
  # will be displayed as "Carl's Terrifyingly-hideous Face"
  carl's_terrifyingly~hideous_face: 
    dice: 8d12
    desc: 9th level. Oh god, oh no, look away if you want to live.
    window: spells