The present invention provides kinase inhibitors, such as compounds of Formula (I) and Formula (II). The compounds may covalently or non-covalently bind a kinase (e.g., Janus kinase 3 (JAK3)). Also provided are pharmaceutical compositions, kits, methods, and uses that involve the compounds for reducing the activity of a kinase and/or treating and/or preventing a condition associated with aberrant activity of a kinase (e.g., a proliferative disease, inflammatory disorder, autoimmune disorder, painful condition, and/or viral infection). (I) (II)