You will find here several software that were developped for various tasks. The source code is provided in the tar ball that can be downloaded (using the download link or here). Please note that no support is provided for them.
RandomTaxa: It will select at random taxa from a phylogenetic tree and output the reduced tree.
GenTree: It will generate random trees from a pure birth process.
BranchCut: It will take a phylogenetic tree and break longest branches until a certain number of taxa is reached.