Supply curve when the marginal cost is zero The supply curve is built as the average marginal cost (MC), when the MC is equal or higher than the average cost (AC)
The marginal cost increases, as a result of the opposite effect of marginal production
In this case, we get a supply curve that's rising from left to right: higher cost per rising quantity 

In the case of marginal cost of zero, I can think of no other case than a supply curve that is equal to AC, and that the AC is dropping, since fixed costs do not change as a result of quantity
And so, we'll receive a curve that's dropping from left to right: lower cost per rising quantity  

Real life cases can be broadcast tv, surpluses in production, "internet economy" etc. 

Am I wrong in my assumption? 
Is there any reference of this type of equilibrium ?
Is it a stable equilibrium ? I mean, since the marginal cost is zero, there is no impact on increasing demand
Took me a bit, but I have figured its out:

The single firm's supply curve is defined as it marginal cost, as long as MC is above it average cost
A firm would not sell below its average cost, since it would loae money, Mathmatically we can define, for the single firm 
S = MAX(AC, MC)

Our basic assumption,for this discussion, is that MC = 0

Under the basic assumption and that costs are positive, obviously, then, the supply curve will always equal AC:
S = MAX(AC, 0), AC > 0
S = AC

The other conculsion from the basic assumption is that the production function, under the costs limit, is completely unaffected by quantity
Intuitively: its costs the same to produce 100 products and 1000 products. 

If the Total costs function, as a function of quantity, is fixed, then the average function is:
AC = TC/x

In that case, we'll get a supply curve, though a very special one:
It'll decrease price as a result of increasing quantity, and prices will aspire to zero. always

Update:
Allowing myself to add a link to an article I wrote on the topic:

Start-Up economics: the disrupt model