Trojka is a falling block puzzle game, somewhat similar to Columns, but using its own matching rules. The game is played in a rather narrow well, of only 5 blocks wide. Blocks fall individually, and need to be matched in groups of three or more horizontally or diagonally, but not vertically (which would be trivial).
At a low enough speed, the game initially feels simple to plan far enough ahead to set up combo after combo and keep the board well under control. Then you get a few wrong colours in a row and start trying to offload them somewhere. Then you forget which combos you were building and block them. Then the game gets faster and panic ensues.
So yeah, typical falling block puzzle game. However, with the very simple setup, it seems to be at the mercy of the exact block selection considerably more than most action puzzlers. That said, I'm sure if someone played enough they could probably figure out a better long-term strategy than my typical flailing. It is a valiant effort for not just cloning another puzzle mechanic, but ultimately not for me.
Trojka was originally released in 1989 for MS-DOS by Maarten Los. It was then ported to PRIMOS in 1990, Windows 3.x and Amiga in 1991, UNIX terminal in 1992, Macintosh in 1993, X Windows in 1994 and OS/2 in 1995. Phew.
Wait, we aren't done yet.
It was then updated for OSX version in about 2010 or so. At least going by the copyright in the plist file. Digging into the help file for that edition reveals there is also an iOS version called Triplo.
Since the X Windows version appears to be the first Unix-based graphical version, that is the date I am including for the article. Several other authors were involved in the ports other than DOS, Unix and Macintosh. Refer to the manual page for more details.
The following is a demonstration of the game from speed levels 3 to 4:
I also have a video of the terminal version on my YouTube channel for anyone interested.
Trojka is slightly more difficult to find nowadays for Linux distros. However, FreeBSD's ports have got you covered for both the X11 and terminal versions. If you aren't a BSD user (gasp!), both the X11 and terminal version can be found at funet.fi as well.
The Macintosh version is still around, in the Macintosh Repository and Macintosh Garden, as well as on funet.fi. The OSX version (32-bit Intel only) can be found at MacUpdate. The iOS version is apparently no longer available, likely removed with all the other 32-bit iOS apps.
I haven't managed to track down any other versions.
More general information on old X games can be found in the Old X Games article.
If the above video does not work for you, it is also available on my YouTube channel.