It is clear that all three tags mean exactly the same thing (except for a few questions - 8 - about Google Cloud Messaging for Chrome, which is a totally different topic, and for which I created a new tag chrome-gcm), but users keep using all three of them in new questions, sometimes even in the same question.
As of 2014/01/14 :
- android-gcm 1146 questions (of which 1062 without google-cloud-messaging and 932 without gcm)
- gcm 673 questions (of which 459 without android-gcm)
- google-cloud-messaging 264 questions (of which 180 without android-gcm)
It is clear that android-gcm should be the main tag. Only about 600 questions are missing this tag.
EDIT : the following part in no longer relevant (I wasn't sure whether to remove it from the question).
It is clear both of them mean the same thing.
Those are too many questions to re-tag, so a synonym would be better. I think apple-push-notifications should be the main tag.
These synonyms were already suggested (some by myself and some by others) but it's hard to get people to vote for synonyms of less popular tags :
(note that apn is not related to Apple Push Notifications and was suggested as a synonym by mistake).
There were already some questions about these tags, but nothing was done to fix this issue :
I ask whoever has the power to either create those synonyms or vote for the suggested synonyms.