I've made a MOD for Command and Conquer 1 DOS version. It uses a preconfigured Dosbox for Windows, Linux and Armv7. You can also try it in your Browser.
C&C Retro Website:
http://divinity.x10.bz/cncretro/
I tried it with my RPi3+Recalbox and it is very playable without overclocking. IPX Multiplayer Networking is also working. I've tested it with my main Linux PC (Lubuntu 18.04) and RPi3. (crossplay should work with Windows, Linux and RPi)

I made a Recalbox "CNCRetro_r03.pc" folder. Unzip "CNCRetro_r03_Recalbox.zip" to your "roms/dos" folder.
C&C Retro r03 Recalbox download:
http://www.mediafire.com/file/bdrvcp1t718xvb8/CNCRetro_r03_Recalbox.zip/file ~11,11MB

A short HOWTO:
You need a Keyboard and Mouse to play.
You will be greeted with two options when launched:

1. START C&C RETRO SINGELPLAYER/Online 1vs1 Modem play
2. START WITH 4 PLAYER Online CLIENT/SERVER

1 --> select when you only play Singleplayer (Modem play DOES NOT WORK)
2 --> CLIENT/SERVER architecture - on the first machine START THE DEDICATED SERVER and then the CLIENTS can connect to the SERVER IP.
Then go to "Multiplayer Game" --> "Network" and make a NEW Game. You MUST make a NEW Game or other Players cannot see or JOIN you.
That's it.

Good times ahead,
-DiViNiTY Studio

The first 3 Command & Conquer titles are "Freeware". Tiberian Dawn, Red Alert 1 and Tiberian Sun were released to the public for free with no licence to them (GPL3, MIT...).
I'm not sure under which license CNC Retro would be. (Public Domain??)

I've made a MOD for Command and Conquer 1 DOS version. It uses a preconfigured Dosbox for Windows, Linux and Armv7. You can also try it in your Browser.
C&C Retro Website:
http://divinity.x10.bz/cncretro/
I tried it with my RPi3+Recalbox and it is very playable without overclocking. IPX Multiplayer Networking is also working. I've tested it with my main Linux PC (Lubuntu 18.04) and RPi3. (crossplay should work with Windows, Linux and RPi)

I made a Recalbox "CNCRetro_r03.pc" folder. Unzip "CNCRetro_r03_Recalbox.zip" to your "roms/dos" folder.
C&C Retro r03 Recalbox download:
http://www.mediafire.com/file/bdrvcp1t718xvb8/CNCRetro_r03_Recalbox.zip/file ~11,11MB

A short HOWTO:
You need a Keyboard and Mouse to play.
You will be greeted with two options when launched:

1. START C&C RETRO SINGELPLAYER/Online 1vs1 Modem play
2. START WITH 4 PLAYER Online CLIENT/SERVER

1 --> select when you only play Singleplayer (Modem play DOES NOT WORK)
2 --> CLIENT/SERVER architecture - on the first machine START THE DEDICATED SERVER and then the CLIENTS can connect to the SERVER IP.
Then go to "Multiplayer Game" --> "Network" and make a NEW Game. You MUST make a NEW Game or other Players cannot see or JOIN you.
That's it.

Good times ahead,
-DiViNiTY Studio