FLOSS pipedreams

3D content creation
Blender (should be mainstream - used in blockbusters)

desktop
GNOME (should replace Mac as THE desktop experience, and then steal the market)

enhanced C Lib
GLib (should be a dependency of most C apps)

CRM/ERP
no favourite candidate (steal SAP's market share)

image manipulation
GIMP (should acquire feature-parity with Photoshop, and then steal the market)

DBMS
PostgreSQL (should acquire feature-parity with Oracle, and then steal the market)

programming language
Python (it's already comprehensive standard lib should rival all in terms of features; its popularity should exceed that of Java on the enterprise and PHP on the web)

OS
Debian (should be THE reference platform for various fields: large corporations, audio/video professionals, software developers, etc)

OS - future
pure GNU, with HURD as kernel (to make Richard Stallman smile)

packaging system
dpkg & APT (should replace RPM)

scientific computing
NumPy, SciPy (feature-parity with R and MATLAB, and steal the market)

sound server
PulseAudio (should be THE implementation of audio API, rivalling Mac's CoreAudio)

VCS
Mercurial (it's written in Python, and will be used by the Python project itself; should steal Git's market)

~~~

[sidenote]
My religious intensity isn't really strong for Mercurial and GTK+, but GNOME acceptance does mean Qt marginalisation.