From the Gramps mailing list discussing portable apps.
PortableApps team has this to say about Gramps 4.x:
"Gramps 4.x - Temporarily on hold pending stability and possible licensing issues"
Stability links to this post http://gramps.1791082.n4.nabble.com/Status-update-goals-and-ideas-td4668....
I have no idea what are the licensing issues they refer to.
and further down the page they speculate that
Note, I suppose the main limitation for the portable app is maybe the bsddb3 licence?
Is that the licensing issue?
And as for stability on Gramps 4.x one of the developers mentions:
I made a list of database corruption bugs:
These stability issues also affect v3.4 and most have a known cause.
Considering we have approximately 20,000 users these problems are rare.
The next major release, v5.0, will give users the option to choose a
different database backend.