Under construction: list of vendors not yet fully populated.

Company NameVendor URL  CC  Products or Services
Advanced Circuits  http://www.4pcb.com  us PCB Manufacture & Assembly
Aerojet Rocketdyne http://www.rocket.com  us Space & Launch Systems
Astronautical Development http://www.astrodev.com  us PQ UHF/VHF & S-Band Radios
Beningo Engineering http://www.beningo.com  us Engineering design & training
Berlin Space Technologies (BST) http://www.berlin-space-tech.com  de CS & Bus components
Blue Canyon Technologies http://www.bluecanyontech.com  us CS & Bus components
Clyde Space http://www.clyde-space.com  uk CS Power & other systems
Freetronics http://www.freetronics.com  au Arduino Compatible Kits
GAUSS http://www.gaussteam.com  it CS Design, Manufacture & Launch
GOM Space http://www.gomspace.com  dk CS Systems & Components
Honeybee Robotics http://www.honeybeerobotics.com  us SmallSat & Exploration Systems
Innovative Solutions http://www.isispace.nl  nl CS Kits, Subsystems & Ground Stations
Leijenaar Electronics http://www.leijenaarelectronics.nl  nl Ham radio transponder (one man)
Masterbond http://www.masterbond.com  us Adhesives, Sealants, Coatings
PocketQube Shop  http://www.AlbaOrbital.com  uk PQ components, launch, & swag
Pumpkin http://www.cubesatkit.com  us CS Kits, 3U Bus, Components, CAD models, Dev & Proto Bds
RadioBro   http://radiobro.com  us CS Radio & Antenna
SatCatalog   https://www.satcatalog.com/  us Online Spacecraft COTS Parts Marketplace
Sensormetrix http://www.sensormetrix.com  us EMF Sensor & Cloaking Systems
Sequoia Space  http://www.sequoia-space.com  co Space rated CS hardware & systems
Solar MEMS Technologies http://www.solar-MEMS.com/en/  es MEMS designers, solar & horizon sensors
Space Micro http://www.spacemicro.com  us Radiation hardened satelite subsystems
Spectrolab (Boeing) http://www.spectrolab.com  us Photovoltaics, Concentrators, Sensors (A Boeing Co.)
Tethers Unlimited http://www.tethers.com  us CS deorbiters, S/W radios, Solar Arrays,Articulator Gimbal, Propulsion, Robotic Arm.
Tyvak  http://www.tyvak.com  us Premier CubeSat Developer. Founded by the CubeSat co-inventor, Jordi Puig-Suari.
        
GMAT-like Software, both Open Source* and Proprietary:
Company NameVendor URL  CC  Products or Services
Boeing (& NASA) * https://ntrs.nasa.gov/citations/19710021202  us  CHEBYTOP: Chebychev Trajectory Optimization Program
AGI   https://www.agi.com/products/stk  us  STK - Proprietarry Systems Tool Kit. (a competing GMAT)
AGI   https://www.agi.com/products/odtk  us  ODTK - Orbital Determination Tool Kit
SpaceWorks  https://www.spaceworks.aero/software/quickshot/  us  QuickShot Trajectory Optimization Software
ESA (NASA Open Source) * http://orsa.sourceforge.net/  eu  ORSA - Orbit Reconstruction, Simulation amd Analysis
Martin Schweiger, creater * https://github.com/orbitersim/orbiter  uk  Obiter 2016 Space Flight Simulator Game
NASA GSFC * http://odtbx.sourceforge.net/  us  ODTBX - Orbit Determination Tool Box
NASA GSFC * https://opensource.gsfc.nasa.gov/projects/JAT/index.php  us  JAT - Java Astrodynamics Toolkit
Chris Laurel, creater * https://github.com/CelestiaProject/Celestia  us  Celestia - 3D Astronomy Cosmological Viewer
NASA GSFC * https://software.nasa.gov/software/GSC-16720-1  us  42 - Attitude & Trajectory Simulation Tool
CS Group * http://orekit.org/  fr Orekit - Java Low-level Space Flight Dynamics Library
Delft University * https://github.com/tudat  nl Tudat - TU delft Astrodynamics Toolbox
a.i. solutions  https://ai-solutions.com/freeflyer-astrodynamic-software  us FreeFlyer - Proprietary Astrodynamics Software
NASA ARC  https://trajbrowser.arc.nasa.gov/index.php  us  NASA ARC Trajectory Browser
Saber Astronautics  https://saberastro.com/  au  P.I.G.I - Predictive Interactive Groundstation Interface
NASA GSFC * https://opensource.gsfc.nasa.gov/projects/emtg/index.php  us  EMTG - Evolutionary Mission Trajectory Generator
        
        
  * Indicates Open Source    
(SEA: 220101)