The application can simply be downloaded by following the link on the login page or searching for "btree" in he google play store. It is available for all devices which support NFC.
With the native android application you got a own side menu, which lets you write and read NFC tags. If you click on write, the link to the current page will be written to the nfc tag. For reading NFC tags there is a special case, if you are on the "quicktool" page and read a tag with following format https://www.btree.at/app/detail/hive/XXXX or https://www.btree.at/app/detail/apiary/XXXX it will select corresponding hive or apiary in the selection. If you read the same tag but you are outside of the quicktool it will take you to the corresponding hive or apiary detail page.
b.tree cannot does not support a offline version. The Android app (and iOS) is the same as the web browser but with a few additional functions (see NFC).