For RNA-seq assembly, see the tools under the group RNA-seq at Galaxy Main (http://usegalaxy.org). These do not create consensus sequence, but rather perform data reduction for expression analysis. Tutorial: https://wiki.galaxyproject.org/Learn/GalaxyNGS101#Reference-based_RNA-seq
A certain type of consensus can be generated with the tools under the group De Novo. Review the tools to see if it is a fit for your input datatype and goals.
For full consensus sequence assembly, see the tools under the category Assembly in the Galaxy Tool Shed (http://usegalaxy.org/toolshed). These majority of these tools are for use in a local or cloud Galaxy (https://wiki.galaxyproject.org/BigPicture/Choices).
How to use the underlying wrapped tools can be found in the help section per-tool, including links to 3rd party software.
Hopefully this helps, Jen, Galaxy team