This is answered in the official wiki:

Like Bitcoin:

  • ripple is a distributed peer-to-peer payment network
  • ripple transactions are irreversible, sent over the Internet, and counterfeit proof
  • ripple uses the same underlying cryptography as Bitcoin
  • ripple has multi-signature support
  • ripple has low to no transaction fees
  • ripple servers can be run by anyone

Unlike Bitcoin:

  • ripple can send any currency
  • ripple can automatically exchange currencies
  • ripple transactions are fully confirmed in seconds
  • ripple allows nicknames and gravatar icons for accounts
  • ripple's reference client is a Firefox and Chrome add on
  • ripple has no block chain download, clients are ready in seconds
  • ripple has no mining or direct monetary reward for running a ripple server
  • ripple has no currency risk as people can hold whatever fiat they want
  • ripple solves the double spending problem with consensus instead of proof-of-work