Bone Shaker lets you choose what dice systems you want to use when you start your session. By default only the normal (d20) dice system is enabled. To enable others simply select the ones you want on the Dice Systems tab:
Although you would normally only want to use a single dice system in one session, Bone Shaker allows you to easily switch between the selected dice systems using the Change the active dice system button (this button will be hidden if only one is selected):
This can be useful if you are using combinations of dice systems, for example using normal (D20) for adventuring and the One Roll Engine for higher level political intrigue. Your favourites and temporary modifiers for each system are stored separately so when you switch between dice systems Bone Shaker will update to show you your favourites and temporary modifiers for the selected system.
Each dice system has a variety of options to allow each one to be tailored to the specifics of the rules of the role playing system you are using.
How to use the different dice systems is described in more detail here: