SVN Seeds are files that when updated in tortoise rebuild the entire SVN tree.
To use extract the zip into your location of choice, right click and hit "SVN Update"
Like magic, the whole tree will be rebuilt.
These links are here because garrysmod.org doesn't seem to like SVN seed files. These are SVN seeds for various projects.

Seed Link	Project Name	Facepunch Thread	Website
SBEP	SpaceBuild Enhancement Project	Thread
PHX	Phoenix Storms	Thread
RD3 NESC	Resource Distribution Necessary		Website
RD3 OPT	Resource Distribution Optional		Website
GCX	GCombat Extended	Thread
SGA	Stargate Overloader	Thread
SGM	Stargate Mckay	Thread
WIRE	WireMod		Website
WIREE	Wire Extras		WM.COM Thread