various federation related links:

mirror (1) uptodate
(wiki) 
systemcomment
servers / instances 
here
GS
view list, or better:
compare some of them (based on selected criteria)
groups 
here
GS
groups on different servers
clients + server themes
here
GS
see the graphical side of GNU social
some usage statistics here
statistics
GS
user / server stats
wishes, ideas by community
here
GS
 http://oracle.skilledtests.com/group/fedgroups 
here
posts by group members
Problems and solutions
here
F
Problems and solutions
here
GS
Pump.io
here
P
Federation
here
wiki category
federated communication platforms
here
various systems which one day
MUST speak to each other
Aspects of federation
here
what does it mean when you install your system?
hosters for your federated system
here
finding a home for you
find users
here
based on: similar interest
MUDs and statusnet
here
M
let's bring 'em together
Twister
here
T
stats, infos about the p2p system
my experiences
howto: twister with Tor
Freenet
here
FN
stats, infos about the p2p system
Trsst
here
TR
stream-style RSS reader (w. built-in microblog)


F = friendica
FN = freenet
GS = GNU social (statusnet)
M = MUDs
P = pump.io
T = twister
TR = trsst


(1) the mirrored page may not always be up-to-date: but it shows you the main info