Ushahidi is a non-profit organization that develops open source technology for disaster response. We've covered how its been used to visualize floods in Queensland, for example.
Above is a brief introduction to its technology for developers.
Disclosure: ReadWriteWeb contributor Pete Warden recently joined parent organization SwiftRiver as we reported here.
CouchDB is great for building Web applications that need to function when Internet connectivity is sporadic. CouchDB sponsor company CouchOne has a case study on how aid workers in Africa are using it to manage health data.
As we reported earlier there's been a spike of Tor usage in Egypt the during the past couple days as the government there has severely restricted Internet access. Many on Twitter are calling for users to host more Tor relays. Here's how to configure one.
Be sure to read the FAQ for running a relay.