First Islam was a religious movement which took,part in the Commission of Ecumenical Translators and which contributed to the Orange Catholic Bible.It seems to have been a remnant or a group claiming to preserve the old terran islam as itbhad been before it's various shifts and splits throughnthe second and Third islamic movement.It's fate after the establishment of Orange catholic ecumenism reamains unknown, but even in post-Butlerian Jihad times it's role and influence in the Known Universe seems to have been only marginal in comparison to younger syncretist belief-systems such as Koranjiyana Zenchristianity or even Buddislam.
Dune Encyclopedia
The Dune Encyclopedia also mentions another seemingly islamic group which attended the commission, which went under the name "the Assemblies of Allah".
Most other apparently islamic-influenced groups either were already secessions or variations of the second or third movement (Muadh Quran Faith, Muadru, Muslim Fideism,Palislam,Sugislam, Sunislam, Sunni, Sunni Orange Co-operative,Sunsufism) or already buddislamic syncretisms (Zenshiite, Zensufi, Zensunni) or syncretisms of either buddislam or second or third islam with other faiths (Buddislamic Christian Church,Hasidislamic Union, New Islambahai Church or the Last Church of Christ, Zensunni Catholic Amalgamation). Their relation to first Islam was dubious or at last interceded.