Trinity is one of the greatest and most original sci fi games ever made. The world is fleshed out very well, and the technology and culture are presented in a fascinatingly realistic manner. I love it.
That said, here's the lowdown.
Trinity has stopped producing print supplements. The last book, Terra Verde: South America and Psi Order Norca, was released as a PDF only. Apparently, the game did extraordinarily well in its first year (1998, I believe), but sales dropped off quickly afterwards. In the Developer Chat in 2000, it was said that the writers were contracted to do several more books, the last of which would be the sourcebook detailing China and the Ministry of Psionic Affairs. However, nothing said that these supplements would ever see true printing- all indications point to the series being wrapped up digitally.
So, for all intents and purposes, whenever that book comes out, Trinity will be dead, unless White Wolf chooses to continue to pay the writers to make more (on PDF, I think the days of printed Trinity are long gone).
That said, you're not too late to pick it up. White Wolf has released "Assortment Packs" on its online catalog. Pack A is about 40 clams and includes the core rulebook, America Offline, Luna Rising, Stellar Frontier, and Shattered Europe, which detail their respective regions and psi orders Orgotek, ISRA, Upeo wa Macho, and the Aescapulian Order, respectively. Pack B costs around 25 and includes the core rulebook, technology manual, and...I forget what else. Either way, they're great deals (I picked up Pack A first, being a sucker for campaign material).
If you need some background info, well, Trinity is a game set in the somewhat near future- 2120. About fifteen years ago, a small group of humans were invested with psionic powers from some unknown source. These seven people, collectively known as the "proxies," were charged with creating orders for others like them and gifted with devices that would allow humans to awaken psionic latency. These "Prometheus Devices" each correspond to a separate psionic discipline, which include Electrokinesis, Biokinesis, Telekinesis, Clairsentience, Teleportation (rare), Vitakinesis, and Quantakinesis (no longer in existence).
This isn't your typical "blasters and starships" sci fi. Interplanatary colonization is barely widespread- the vast, vast majority is still chained to Earth. The concepts are explained in a thoughtful and scientific manner- the words "noetic theory" spring up quite often, and I'm pleased to see them. The designers actually made an effort to give the world some serious verisimilitude, which is more than can be said for the average sci fi game.
All in all, a wonderful addition to your collection. I'd put it up there with Vampire, Exalted, and SLA Industries as one of my favorites.