Download the version for your system. File size is about 5 MEG.
Both, app and database are so compact that you can sync it via Dropbox/Google Drive/... Just move the whole Bibliographix directory to a synced directory after installing. To stop syncing, move the directory or exclude it from syncing.
Using multiple operating systems
Each operating system (Windows, MacOS, Linux) has its own native version. These versions have slightly different names and happily coexists in one directory. When using the software in the cloud you may use a Windows system at office and a Mac at home accessing the same database.
Download the Linus version you need(64bit, 32bit, Raspberry Pi)
The download is a zip file. Copy it to the directory to install and unzip.
Start bibliographix32 or bibliographix64 or bibliographix_rasp (whatever applies)
Very likely the program will not run after starting as Linux does not recognise that the file is executable. If so, pop up your file manager and edit the properties of the file and switch on "executable" and try again.
Setup file name is setupbx11.exe. Doubleclicking it will start the setup.
Most applications suggest /program files as path to install. Bibliographix suggests \documents. This is unusual but due to the fact that Bibliographix is a portable application that is able to run on an usb stick or the cloud. To do so it needs full access rights to files in its own directory which is not granted in /program files.
You may install the app in any other directory. Make sure though you have complete access rights.
The setup file is a zip file. Download it and move it to the directory in which to install. You can open this zip file like a normal directory. You will find a bunch of files and directories. Click the app file "Bibliographix"
Very likely your computer will tell you that Bibliographix cannot be opened as it comes from a unverified developer (translated from the German phrase). In case you are not familiar with this message: Apple wants you to use the Apple app store exclusively. Developers need to accept some Apple rules to be allowed to upload to the store. This has advantages and disadvantages. These rules collide with freely available software like Bibliographix and so I'm not a verified developer. This is what the message tells you.
To bypass this message, click OK, then press the CTRL key while clicking Bibliographix again. This will display a menu. Click "open". You will probably receive a message like this software comes from an unverified developer. Do you REALLY want to open it - Yes you do. This setting is stored with the system so you will have to undergo this procedure only once.