Best Open Source (Free) Softwares for Architects

Blender 3D - best for animation and modelling like Maya and 3ds Max
Unity3D - best for game development, tools development, interactive visualization
Processing  - best computational, parametric, programming tool
Gimp - best photo editing tool like Photoshop
Synfig - Great presentation tool like Flash
Lightworks - Best Video editing tool.
EnergyPlus - Best simulation tool can be used in a combination with Sketchup, ecotect, designbuilder, processing and many other software packages.
Prezi  - Probably one of the Best Presentation Tool ever created
Lucidchart - A tool for generation of conceptual flow charts.
Apache Open Office - A free Office, that can be replaced with MS Office.
Celtx - an effective tool for writing your stuff.
CV maker - make your cv in minutes.
Wolfram Alpha - one of the most amazing tool for calculations graphs, and most of the usefull stuff. Just try it once.
Hitfilm 3 - Best movie making software.
QCAD -  Free drafting software.
Jyupyter Notebook - Awesome tool for data visualization using python.
Canva - Online Sheet composition, poster , graphics tools.
Picktochart - Online infographics, reports, presentation tool.
Studio Sketchpad - Free online JAVA compiler
ISSUU - Free Portfolio hosting website
Unreal Engine - Free game design software for interactive visualization.

Best Android Free Apps for Architects

Design Dimensions - Standard dimensions of most common architectural entities

Mobile Sketchbook - Android version of Autodesk Sketchbook
Autocad WS - Autocad
Measure and Sketch - Live measuring and sketching tool
Construction Helper - Good for calculating areas and volumes.
Handyman Calculator - Best construction calculator of all. And most important tool for Architects.
BuildApp - Best for creating floor plans and can be visualised in 3D.
House Plans - Free readymade residential floor plans.
Smart Measurement Tools - Tremendously efficient and time saving tool.
Geek Tool Light - Best tool for survey and leveling.
Expense Manager - Manage your Expenses.
Construction Estimator - Simple estimator
Feets and Inches Calculator - As name says. Simple yet powerful.
Diary of Success Puncher - Keep track of your daily progress.
Day Counter - Days countdown app