XShisen is an implementation of the Shisen-sho variety of Mahjong solitaire. In this variety, pieces are arranged into a single rectangle and can be removed if they can be connected by three horizontal/vertical line segments (as illustrated in the above screenshot). This game provides three different board sizes and the option to enable/disable gravity, though the minimum board size still uses a full Mahjong tile set. It can be difficult without some careful planning.
Most sources credit the TAMTEX arcade game, Shisenshou Joshiryou-Hen/Match It as originating this game style; I can't find any mention of rules for a physical Mahjong solitaire game that predate the arcade game.
This specific version is written by Masaoki Kobayashi for Linux, Solaris and HP-UX in 1995, with artwork from Takayuki Akiyama and Mario Weilguni. It uses either Motif or Athena widgets.
The following is a typical unsuccessful play of the game on the standard board size, with gravity enabled:
XShisen is still packaged in Debian. If you are not on a Debian-derived distro, and your distro does not package it, you should be able to re-build the Debian source package. The official website is offline, but it can be browsed via archive.org for some additional information.
More general information on old X games, including build tips 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.