Rambam and Shavuos

 It was interesting researching what Shavuos is in the prime sources

The Rambam apparently ignored the topic

The Torah describes it as a Harvest holiday which is one reason for reading Ruth

The Shulchan Aruch descibes it as the 50th day of the omer

Shulchan Aruch (O C 494) The fiftieth day of the count of the Omer is the holiday of Shavuot.  The prayer service is like the holiday of Passover, rather we say "the Holiday of Shavuot, the time of the giving of our Torah".  We say full Hallel.  We take out two Torah scrolls and read in the first one of five [sections] from "The third month" until the end of the order.  The Maftir is read in the second scroll, "On the day of the first fruits".  As Haftorah we read the chariot of Ezekiel, and end with the verse "and the wind took me up." 

Notice it says it was the time of the giving of the Torah to which the Magen Avraham famously notes that we hold that the Torah was in fact given on the 51rst day of the Omer 

There seems no mention of the Rambam concerning this day

A possible explanation is the following

Rambam (Hilchos Melachim 9:1) 

Six precepts were commanded to Adam:

a) the prohibition against worship of false gods;

b) the prohibition against cursing God;

c) the prohibition against murder;

d) the prohibition against incest and adultery;

e) the prohibition against theft;

f) the command to establish laws and courts of justice.

Even though we have received all of these commands from Moses and, furthermore, they are concepts which intellect itself tends to accept, it appears from the Torah's words that Adam was commanded concerning them.

The prohibition against eating flesh from a living animal was added for Noah, as Genesis 9:4 states: 'Nevertheless, you may not eat flesh with its life, which is its blood.' Thus there are seven mitzvot.

These matters remained the same throughout the world until Abraham. When Abraham arose, in addition to these, he was commanded regarding circumcision. He also ordained the morning prayers.

Isaac separated tithes and ordained an additional prayer service before sunset. Jacob added the prohibition against eating the sciatic nerve. He also ordained the evening prayers. In Egypt, Amram was commanded regarding other mitzvot. Ultimately, Moses came and the Torah was completed by him.

In other words Rambam views the giving of the Torah basically as an extension of the 7 mitzvas given to Noach  This seems to be a minority view