%0 Journal Article %T Noncommutative symmetric functions VI: Free quasi-symmetric functions and related algebras %A G. Duchamp %A F. Hivert %A J. -Y. Thibon %J Mathematics %D 2001 %I arXiv %X This article is devoted to the study of several algebras which are related to symmetric functions, and which admit linear bases labelled by various combinatorial objects: permutations (free quasi-symmetric functions), standard Young tableaux (free symmetric functions) and packed integer matrices (matrix quasi-symmetric functions). Free quasi-symmetric functions provide a kind of noncommutative Frobenius characteristic for a certain category of modules over the 0-Hecke algebras. New examples of indecomposable $H_n(0)$-modules are discussed, and the homological properties of $H_n(0)$ are computed for small $n$. Finally, the algebra of matrix quasi-symmetric functions is interpreted as a convolution algebra. %U http://arxiv.org/abs/math/0105065v1