These categories are somewhat arbitrary; many of these projects are multi-faceted.
Boston Microtonal Society - founded 1998; permanent chamber ensemble NotaRiotous founded 2005; spring and fall concerts.
British Harry Partch Society (????-????)
OddMusic Urbana-Champaign (Illinois)- instrument-building, scale-building composers collective, with emphasis on face-to-face musical meetings.
Microtonal Projects Ltd. (UK) - founded 2004 by Drs. Bousted.
Project XVII (Lima-Perú) - 17 edo and microtonal harmony.
Stichting Huygens-Fokker (Amsterdam) - promoting especially 31-tone music. well-maintained website with increasingly frequent events!
The Xenharmonic Alliance (19??-19??) - Ivor Darreg's mail-driven network of exchanging microtonal music and ideas.
UnTwelve (Chicago) - a Midwest-based project offering concerts, listening parties, and a composition competition.
Ekmelic Music Society/Gesellschaft für Ekmelische Musik (Austria), main focus is on 72edo, overtone music.
Microtonal festivals and events
Just Intonation Network (Bay Area) - in need of assistance in organizing since spring 2006!
Microfest (LA area) - Annual festival founded in 1997.
MMMDay06 (internet, 4/8/2006) - a convergence of microtonal music making. Final product: a podcast.
Music for People and Thingamajigs Festival (Bay area) - Annual festival founded in 1997, focused on odd instruments and tunings.
Xenharmonic Praxis Summer Camp (West Virginia) - Summer camp for microtonal composition and performance started in 2011.
Microtonal Record Labels
split-notes - Microtonal-with-a-beat Netlabel.
Microtonal Record Shelf (?)
Xen-Arts - Microtonal Netlabel
Spectropol - small-run/netlabel; not exclusively microtonal but very xen-heavy
Microtonal media, publishing, archives
Frog Peak - artist-run composers' collective dedicated to publishing and producing experimental and unusual works.
The Microtonal Activist (2001) - an e-zine by Jacky Ligon.
http://www.tolgahancogulu.com/en/microtonal-guitar/ Tolgahan Çoğulu's microtonal guitar research, adjustable frets are used, cooperation with John Schnieder:
Quartertone Marimba (Oslo, 2004-2008) - Ph.D. project by Kjell Tore Innervik
SeventeenTonePianoProject (Houston, 2006-2008) - four concertst using pianos tuned to 17 equal divisions of the octave.
Bohlen-Pierce Clarinet Project - by Stephen Fox.
Alternative Tuning Projects (London, 1998) - Patrick Ozzard-Low's study and proposal for 21st-Century Orchestral Instruments.
Mini-initiatives on this wiki:
ProgressReport: tell your story!
MMMMonth07 - a proposal/brainstorm that wasn't acted upon.
Porcupine Album Project (2012)
Sisters to Microtonality
DIY instrument making (including oddmusic and junkmusic)
a capella music (including barbershop)
music therapy / spiritual music / meditative music
derriere-garde music (alternate-history, neo- )
overtone music (see the Overtone Music Network)