Crabgrass advertises itself as “a software libre web application designed for group and network organizing, and tailored to the needs of the global justice movement”.

Crabgrass is the next generation of social software, we call it (d)emocratic social organizing. Our goal is to facilitate and help unify grassroots social movements, in this country and around the world. Currently an elegant suite of groupware tools (wiki, task list, personal messaging, asset tool, straw poll, ranked voting tool, discussion board, and chat room) embedded in a social software platform, Crabgrass allows individual users to easily manage and participate in multiple groups from one platform.

Crabgrass is written in Ruby on Rails, and hosted by Riseup.net, a collective that describes itself as

an autonomous body based in Seattle with collective members world wide. Our purpose is to aid in the creation of a free society, a world with freedom from want and freedom of expression, a world without oppression or hierarchy, where power is shared equally. We do this by providing communication and computer resources to allies engaged in struggles against capitalism and other forms of oppression.

This is not SaaS, but a downloadable package that can be run on your own server. It looks interesting, and well worth supporting.