When one need an application for work it is always a good idea to check the open source world and the talented people coding there.
Not only the sources can actually be checked to avoid some nasty spying and external company control on your system, but most are not some low level applications, but often are as feature packed as the commercial alternative :
Want a valid and good alternative to Office ?
Open Office
Want a valid and good alternative to high level modelling softwares ?
Blender
Want a valid and good alternative to Photoshop ?
Gimp
etc ... etc ...