features that ZDoom has that are not found in the standard Doom originally released by id:

• Supports all the editing features of Hexen. (ACS, hubs, new map format, etc.)
• Supports most of the BOOM editing features.
• The vast majority of Doom limits are gone (including the evil visplane overflow).
• Free look (look up/down).
• High resoulutions (with optimizations for modern processors).
• Translucency (regular and additive).
• A console.
• More music formats: MOD, XM, IT, S3M, MIDI, and MP3 as well as MUS.
• Better mouse support.
• Limited UDP (Internet or LAN) networking inherited from Linux Doom.
• Quake-style key bindings.
• Jumping.
• Crosshairs.
• Walk over/under monsters and other things.
• Runs under Windows 95/98, Windows NT, and Linux

License: free

Additional System Requirements: svgalib or SDL