I like free & open source so for Windows and OSX, you could try fre:ac. You'll have to go into General Settings | Encoders and change the Encoder to FLAC. Just tried it & seems to be buggy on my Mac though could be fine on Windows.
fre:ac - free audio converter
This might be a better choice for Macs:
XLD download | SourceForge.net
And an alternative for Windows:
CUERipper - CUETools wiki
Only for Macs, try TeslaTunes. It'll copy your iTunes playlists and/or other music library, automatically converting Apple Lossless to Flac.
Tesla Tunes by tattwamasi
I ripped the DVD-Audio using DVD-Audio Extractor.
DVD Audio Extractor -- Full featured DVD audio ripper for your easy use
Note that DVD-Audio has been considered extinct since about 2007 but was a great way to purchase audiophile quality music. Now there’s HDtracks, PonoMusic, eClassical and many other websites but the selection is limited.