Open source Architectural designing software download

[Akhlaakh]

Hello,

Sir, I want to download a free open source architectural design software because the software like Autocad are too costly for personal use. I want to learn it for just purpose of understanding and working on hobby things. So I can't buy that much costly software and comes in many thousand dollars. So my aim is to find a open source version of similar software so that I can learn techniques and also terminology of architectural designing. I am student and also can't afford those costly software. Please suggest me where I can start ?