As the other answers/comments have indicated almost every available genealogical program supports import and export of Gedcom files. With this said two warnings 1) There is currently no automatic way of keeping your online and offline information synchronized - once you upload you will either need to update both your personal records and your wikitree records or, you will need to merge every record that you upload in duplicate. 2) even if you prepare your files offline, when you upload the files the biographies will still need to be edited manually at some point. My oft-cited personal preference is to build wikitree profiles from scratch - but what works for me, doesn't work for everyone.
With this said I am a stong proponent of GRAMPS and GRAMPS Portable - it is perhaps less user friendly to install and learn, but has a wide variety of features I have not seen in other free software; as with most things it becomes easier to use as you gain experience with it. GRAMPS also has some of the best printed reports i have seen in a free program.
GRAMPS portable edition is the only genealogy software that I am aware of that can be run from a USB key as a portable app with no need to install so you may be able to use it on public computers at libraries and archives if needed.
GRAMPS: http://gramps-project.org/
GRAMPS portable edition: http://portableapps.com/apps/education/gramps_portable