Shulchan Aruch, OC 236:3: If someone discovered a group that had already read [the evening] "Sh'ma" and is about to say amida [of maariv], then he should say amida with them and then say "Sh'ma" ...
If one needs to daven mincha and the only minyan that is close by is davening an early maariv can one daven their mincha shmoneh esri with their maariv shmoneh esri and then daven maariv with a ...
In Maariv after Shabbos we insert אַתָּה חונַנְתָּנוּ into the Amidah. In some siddurim the word בהם is introduced making it read אַתָּה חונַנְתָּנוּ לְמַדַּע תּורָתֶךָ. וַתְּלַמְּדֵנוּ לַעֲשות בהם ...