What's the genre of your book? I have a couple lighter-weight RPGs to offer as suggestions.
FATE - you have skills ranked as things like mediocre, expert, poor, etc. (don't recall exact terms). You roll dice to determine how well you do as modifiers (+/-/0) to your skill or attribute when appropriate. Fairly freeform character creation and play. Genreless. You can make it fit almost any genre.
Dread - This is horror focused. The mechanic is a Jenga tower. If a player wants to do a non-mundane task, they pull a block, if the tower falls, that character is out of the game (dead, went mad, whatever, you choose). Tension develops as the tower gets harder to pull from. Ebook is $10-20, can't recall, got it for free for buying the print book at a convention. Very lightweight, while horror focused it is otherwise independent from your setting. Create character sheets describing their history, their skills then are "what does it make sense for them to know". Does it make sense for the programmer to be a sharpshooter? Maybe not, maybe a difficult shot requires two pulls for them. OTOH, a soldier character may only need to pull if the shot effects the story more significantly. You can wing it, but be consistent with your players.