VLC Player Plays pretty much any audio or video file you care to throw at it. Includes a CSS descrambler for playing DVDs.  Although it’s VERY good, it’s not perfect - some things still play better in Windows Media Player.
 MPC - HC "Media Player Classic - Home Cinema" is intended to feel like Windows Media Player 6.4 (from Windows 2000), but includes modern features and codecs. While less format-compatible than VLC, sometimes it runs better on slow platforms.  It also works with some formats that VLC doesn't.
 Audacity A full-feature wave form editor and sound production facility. Also good for simply recording from any audio input. Unless you’re a professional sound engineer, this should cover all your sound editing needs.  Due to licensing issues some codecs may need to be downloaded separately.
 CDex A simple, well designed “CD Extractor” for ripping CDs to MP3 and various other portable formats. Although nobody buys CD's anymore, this can turn an old CD collection into a great bunch of MP3's.  Includes “paranoia” modes to minimize data errors from old/worn/scratched CDs.
 ImgBurn Reads/Writes CDs, DVDs, BluRays, and ISO/UDF image files. Can rip encrypted commercial DVDs if “DVD43” driver is loaded (for legal use only, of course) While a very capable tool, usage is not always obvious: e.g. to make an audio CD you select “Tools - Create CUE file” from the main menu.  The last version was released in 2013 - so OS compatibility may become an issue.
 HandBrake This video transcoder coverts from typical optical input formats to a range of file-based audio/video formats. Similar to ImgBurn, it relies on the "libdvdcss" library (included with VLC) to deal with DVD copy protection. While it can handle BluRay disks and images, you would need a simple tool like Free Blu-ray Decrypter or full featured commercial app like AnyDVD HD to circumvent copy protection (again, for legal use only).  
 DVD Flick Very simple DVD authoring tool that transcodes a wide variety of multimedia files to DVD VOBs. Actually uses an internal copy of ImgBurn to write the DVD image to a disc.  Does not appear to support Blu-Ray authoring yet.