This is from a time when phones were barely getting cameras, and were very limited in multimedia functionality. MP3 Players were popular media device, but this device adds video playback on its 4.3″ 800 x 480 resolution touch screen. The screen was very high resolution for the time.
They call the category of this device a Portable Video Player (PVP).
The battery was Lithium-ion Polymer technology that can power it for up to 5.5 hours video playback or 17 hours audio playback.
This device also had plugins ($20 each) to unlock HD Video, Internet radio, Dish Network, web browser and more. In order to browse the web on the WIFI, you needed to buy a $30 plug in for Opera Web Browser. The browser does include Adobe Flash compatibility, and auto detects video on websites such as YouTube or Dailymotion and puts it full screen automatically. It was able to play MP3, WAV, WMA (even with DRM), but you need a plug in for AAC. Video can be in MPEG-4, WMV or AVI at 30FPS, but formats like H.264 and MPEG-2/VOB were $20 Plug ins.
There was also a $99 dock and a $69 DVR travel Adapter which can record TV shows for playback on your TV or this portable device.
Sources:
https://www.cnet.com/reviews/archos-605-wifi-review/