Before Spotify, before iPods, and before iTunes, there was Winamp. The media player launched in 1997 and when I had a Windows PC, it was my go-to music playing software. It could play MP3, MIDI, AAC, M4A, FLAC, WAV, and WMA but it was one of the first major music players to suppose Ogg Vorbis, making it a great underground pick too. Winamp also let you apply custom skins to jazz up its UI, burgeoning a community of skin makers.
Fast forward to the 21st century and we now have the Winamp Skin Museum, which lets you infinite scroll through 65,000 Winamp skins. According to Wikipedia, there were only 3,000 skins in 2000.
The themes are spectacular covering the likes of Zelda, Mountain Dew, Garfield, and Jennifer Love Hewitt.