Custom Friends Capes
The 1.10.2 version requires p455w0rd's Library v1.0.5 or greater. The appropriate version can be obtained here.
The 1.7.10 version requires p455w0rd's Library v1.0.4 or greater. The appropriate version can be obtained here.
All capes are added via commands and tab-completion is fully supported.
SSP is supported as well to give yourself a cape.
Commands
Single Player
/cape set <url or cached texture>
/cape remove
/cape texturelist
Multiplayer
/cape set <name> <url or cached texture>
/cape remove <name>
/cape list
/cape texturelist
Command Descriptions
texturelist - lists cached texture names
list - lists all players who have capes via this mod
remove - removes the cape from the player
set - sets the cape to the specified url or cached texture name
Texture Caching
When URLs are added, they are cached. The cached name is the file name minus the extension, so http://somesite.com/some_cape_file.png would be some_cape_file in it's cached version.
These cached texture names can be used in place of URLs in commands.
Permissions
No need to ask for permission to include this in a mod pack or to use it on a server.
Note on Mojang EULA
So long as you are not a server owner selling access to these capes, it is perfectly acceptable to use this mod on your server as stated by the Mojand EULA.
Most recent Mojand EULA can be found here
Commercial use guidelines can be found here
2014 Commercial use follow-up can be found here