I suggest the GNU Affero General Public License v3 which means that anybody running Kiwi would have to make the source code/their modifications available under the AGPL as well. Generally, people won't be "distributing" a modified Kiwi, just running it so this best to get changes into the open.
Other options include:
Standard GNU GPL that we all know and love
EUPL - The EU Public License, compatible with the GNU GPL via CeCILL v2, tailored towards EU copyright law.
KiwiIRC needs some sort of copyright license.
I suggest the GNU Affero General Public License v3 which means that anybody running Kiwi would have to make the source code/their modifications available under the AGPL as well. Generally, people won't be "distributing" a modified Kiwi, just running it so this best to get changes into the open.
Other options include: