For browsing help files, the Dash application is very useful on Mac and iOS.
Here you can click to launch Dash and install our plugin help:
MBS Xojo Plugin and MBS FileMaker Plugin
You can download the archives manually on our website:
FileMaker and Xojo (Real Studio).
You can also add Xojo documentation itself to your dash set, see download in preferences dialog.
For FileMaker you find the docsets for v15 here: FileMaker Dash Docsets
Feedback is welcome.