What do the derived functors of the symmetric powers look like? I understand that this is related to the homology of the symmetric groups, but I don't know a reference for that. 


Namely, I'm interested in the homotopy groups of the free simplicial *commutative* ring on a simplicial set. Let $X\_\bullet$ be a simplicial set; I'd like to know the homotopy groups of $\mathbb{Z}[X\_\bullet]$. This is the symmetric algebra on the free simplicial abelian group $\mathbb{Z}X\_\bullet$, which is weakly equivalent to a product of Eilenberg-MacLane simplicial abelian groups corresponding to the homology of $X\_\bullet$ (and is cofibrant).
In particular, we have a weak equivalence of simplicial commutative rings
$$\mathbb{Z}[X\_\bullet] \simeq \bigotimes \mathbb{L} \mathrm{Sym}^\bullet K( H\_n(X\_\bullet, n)),$$
which brings up the question of what $\mathbb{L} \mathrm{Sym}^\bullet$ looks like. 
 Tyler Lawson points out in answering [this question](https://mathoverflow.net/questions/45273/what-facts-in-commutative-algebra-fail-miserably-for-simplicial-commutative-rings) that the answer is somewhat complicated and describes it in low degrees. 


Is a complete answer known? 



Derived functors of symmetric powers
The homology of all of the symmetric groups together is well understood, as Tyler says.
Taking mod $p$ coefficients, that is the special case when $X = S^0$ of the calculation
of $H\_\*(CX)$ as a functor of $H\_\*(X)$, where $C$ is the monad on based spaces associated 
to any $E\_{\infty}$ operad of spaces. The calculation in this form is given as Theorem 4.1, 
page 40, of [Cohen, Lada, May. The homology of iterated loop spaces, SLN Vol 533. 1976]
which is available on my web page. The functor is not all that complicated, but you do 
have to understand the Dyer-Lashof operations, which are very much like Steenrod
operations and can be seen with those as special cases of a general construction of 
Steenrod operations [A general algebraic approach to Steenrod operations. In SLN Vol. 168.
1970] also on my web page. The paper of Bisson and Joyal cited by Tyler gives a reformulation
of this functor in the case $p=2$. If you want the integral homology, that is a mess to write
down in closed form, but the mod $p$ Bockstein spectral sequence of $CX$ is entirely determined by 
that of $X$, as explained in Theorem 4.13 op cit above, so that integral information is also
available. It is worth emphasizing that viewing the homology of symmetric groups as a special
case of $H\_\*(CX)$ substantially simplifies both the calculation and understanding the answer.


