Below is a selection of useful resources I've been bookmarking that may be of some use to you. I'll update this as I go. Feel free to submit your own contributions.
Bombjack
Very useful site FULL of old books, cd material. Really a very useful site archiving books out of print longer than I've been alive. Everything from the Commodore VIC-20, ZX Spectrum, MS-DOS, Turbo Pascal.. If it's old and retro this site probably has it!
WinWorld
Nice collection old abandonware software. A lot is for DOS but they have plenty of other software for other computers as well.
DOS Haven
Great site for DOS lovers. Full of libraries, tools, software and games.
PCjs Machines
Has web emulators and books related to DOS.
Bombjack
Very useful site FULL of old books, cd material. Really a very useful site archiving books out of print longer than I've been alive. Everything from the Commodore VIC-20, ZX Spectrum, MS-DOS, Turbo Pascal.. If it's old and retro this site probably has it!
WinWorld
Nice collection old abandonware software. A lot is for DOS but they have plenty of other software for other computers as well.
DOS Haven
Great site for DOS lovers. Full of libraries, tools, software and games.
PCjs Machines
Has web emulators and books related to DOS.
Creator of The Retro Dev.. Living inside of FreeDOS and Linux.
System Specs:
OS: FreeDOS 1.3
CPU: AMD AM5x86-P75+ @150mhz
Memory: 64MB
Sound: Sound Blaster AWE32, Roland SC-55 Sound Canvas
Keyboard: Model-M
HD: 32 GB MicroSD
GPU: S3 Trio 64
System Specs:
OS: FreeDOS 1.3
CPU: AMD AM5x86-P75+ @150mhz
Memory: 64MB
Sound: Sound Blaster AWE32, Roland SC-55 Sound Canvas
Keyboard: Model-M
HD: 32 GB MicroSD
GPU: S3 Trio 64