GATK version 4.beta.2 (i.e. the second beta release) is out. See the GATK4 BETA page for download and details.
MuTect v1 -- Reliable and accurate identification of somatic point mutations in high-throughput sequencing data of cancer genomes. Note that a new version called MuTect2 has been integrated into the GATK as of version 3.5 as a beta preview. Once MuTect2 moves out of beta status, support for the original MuTect will be discontinued. You can find the MuTect2 tool doc at https://www.broadinstitute.org/gatk/guide/tooldocs/org_broadinstitute_gatk_tools_walkers_cancer_m2_MuTect2.php