What are the known software tools for the EV3?
The graphical software that ships with the EV3 set can program both EV3 bricks and older generation bricks. We assume that this means NXT 1.0 and 2.0 bricks. However, it is unlikely that NXT-G will work with EV3 bricks as EV3 bricks run a custom build of Linux, whereas older bricks run a custom firmware.

LEGO will create an offical app for both Apple and Android devices, but other app developers will be able to use the API to interface with the EV3. There will most likely be some documentation available (as it was for the NXT), and perhaps a SDK available for download.