& when I say “Traveller”, I generally mean “classic Traveller”. Sometimes abbreviated “CT”.
Top 10 things to know about classic Traveller when I’m ref
Aptitudes: What characteristic scores give DMs for each career?
A summary of CT self-improvement
Far Future: Marc W. Miller’s company. (MWM is the creator of Traveller.) Sells CT reprints as well as reprints of other GDW products.
BeRKA has a map of the Spinward Marches as well as individual subsector maps & world data on his Zhodani Base site.
QLI/RPGRealms: Publishes T20 (a d20 version of Traveller). Also publishes a cool little reprint of CT books 1-3. Most of their T20 supplements are CT compatible.
Citizens of the Imperium forums: Forums for discussing Traveller in all its incarnations. Hosted by QLI/RPGRealms.
GURPS Traveller: Steve Jackson Games publishes a GURPS version of Traveller. (Sometimes abbreviated “GT”.) Some of the supplements can be used with CT.
Traveller5: This site has forums to discuss & playtest documents for the fifth version of Traveller. With two active Traveller licensees (GT & T20) & the ongoing CT reprints, don’t expect T5 to be out anytime soon. It is in the works, though.