According to wikipedia:

  "Squatting consists of occupying an abandoned or unoccupied space or building that the squatter does not  really pay or even has some kind of permission to use."



There has been a long debate about Squatting, some people are against it and some people support it.  Leaving those arguments apart, Berlin is famous for the great number of squats and housing projects. Some of them represent cultural and political movements.

You can find information about each one directly on their site, each group represents itself differently, for example one of pages listed below  describes itself as:  "Anarcha-Feminist, Queer, FLT Collective and Social Living House-project".
(Most of them are only in German but using Google chrome you will be able to translate them)......

http://stressfaktor.squat.net
Schwarzer Kanal
Boedi9
Köpi
Kastanieallee86
Liebig34
New Yorck (im Bethanien)
Projektraum48
Rauchhaus
Rosa Rose Garten
Sama32
Tommy Weisbecker Haus

If you wish to donate blood, help someone and earn some few bucks, here are some of the links:

http://trans.charite.de/service/blutspende/
http://www.haema.de/
http://www.drk-blutspende.de/blutspendetermine/

 Yoga is one of the most loved activities in the city. It not only helps you to improve flexibility, it can also strength your muscles. This can protect you from arthritis and even back pain.

 
 Here is a list of some yoga courses in Berlin:

http://www.adyayoga.de (you pay what you want!)
http://yellow-yoga.com/ (different options for your yoga class)
http://www.bikram-berlin.de/ (courses around 10 euros)
http://www.sunyoga.de

 
And goods news is that most probably your insurance company will be able to pay up to 80% of your yoga class!..... Just call them and ask them, they often prefer that you continue a healthy life than paying for medicines or a hospital. This is done more often in Germany each year :-)

Good luck finding your yoga course!

Surfing in internet I found two nice places where you could repair your mac, in a cheap way:

http://www.betterworx.de/

or  a place highly recommended by other people:

http://www.freakinmacstore.com/

and recently a new option:

http://www.keenley.com/service

If you are planning to brew your own beer you should know that German government allows up to 200 liters of home brewing,  this means you can drink create and make a lot of beer if you are not planning to sell it :-)

http://en.wikipedia.org/wiki/Homebrewing