thanks for your interest in our product. BoxCryptor for Windows supports the requested feature. When you enter the password, you can specify that BoxCryptor should remember this password. BoxCryptor then stores the password encrypted in a secure way (using built-in Windows routines) and you will not be asked for the password at the next start.
By default, the encrypted folder is mounted automatically when BoxCryptor starts and BoxCryptor is started automatically when the computer is switched on.
We do not yet have a native BoxCryptor version for Mac but our encryption is compatible with the open source software EncFS. We're currently working on BoxCryptor for Mac and we expect to release a first version in approx. 2 weeks. Until then, you'd have to use the EncFS installer we provide on our download page: http://www.boxcryptor.com/download/#platform_linux_dl
Hope I could help you.