MUSCLE (multiple sequence comparison by log-expectation) is public domain, multiple sequence alignment software for protein and nucleotide sequences.[1][2]
MUSCLE is often used as a replacement for Clustal, since it typically (but not always) gives better sequence alignments; in addition, MUSCLE is significantly faster than Clustal, especially for larger alignments (Edgar 2004).
MUSCLE is integrated into Geneious Pro and MacVector and is also available in UGENE as a plugin.