You can connect multiple computers/laptops via LAN/Local Network and share one folder so that it is accessible on all devices as: //shared-folder/data/
Now follow these steps:
1. Close Book Keeper in all your devices.
2. Locate your company file. By default company file is saved on Desktop, cut that file and paste into //shared-folder/data/ location.
3. Open Book Keeper and choose 2nd option: Open Company.
4. Browse to //shared-folder/data/ location and select your company file.
a. If you are using same company across various devices, enable User Management, we strongly recommend to use one user at one device. Go to Settings > User Management. Video tutorial: https://www.youtube.com/watch?v=ueg4IsToKe4
b. This Sync Over LAN will work only on PC/Laptops, this method won't sync with Book Keeper Mobile.