The standard version of Blast uses a text (command line) interface, but NCBI also makes a version that runs through a web server, even on your own machine. I haven't tried their Mac version yet, but if you wish to give it a try, it's in the same directory as above, the file starts with the text 'wwwblast'.
An alternative to NCBI Blast is WU-Blast, which claims to be faster and more sensitive. MacOS X versions are available under licence (free for academics) from the above page. The uncompled 1.4 version is also available freely.