Love your Macintosh? Love your mobile phone or PDA? Would you like your data synchronized?
Apple has built-in their "iSync" in Mac OS for some time, but new in version 10.4 (Tiger) they provide "Sync Services". Sync Services lets programmers move data seamlessly between: computers (such as multiple Macs), devices (such as mobiles phones and PDAs), and network services (such as .Mac).