If variety is the spice of life, then the Fort Worth Opera’s “Frontiers” is a well-seasoned dish. For the second day in a row, the company presented four new works Friday afternoon, and once again each was quite unlike the others.The workshop sessions of 20-minute excerpts are run in conjunction with the company’s Bass Hall festival, which means that a group of professional singers are available to give voice to new roles. Pianists take the orchestral parts, and the venue is the modest-sized McDavid Studio.Friday’s subject matter included the rise and fall of Lady Macbeth, the last days of baseball’s Negro League, a mysterious parable about love in a confused-gender world, and life in Eudora Welty’s Mississippi. The musical styles were a varied as the subject matter.Starting the afternoon impressively was “The Mortal Thoughts of Lady Macbeth,” with music by Veronika Krausas and libretto by Thomas Pettit. The highly original vocalizing — wordless syllables, sung passages, spoken text, whispers, soft wailing — created a sound environment that was eerie yet strangely compelling.The four-character piece -- Lady Macbeth and the three witches -- was beautifully realized by Elizabeth Westerman, Jeni Houser, Kristen Lassiter and Amanda Robie, with strong assistance by pianist Stephen Carey and direction by conductor Tyson Deaton.A short chamber opera, the work was given in its entirety.“The Summer King,” with music by Daniel Sonenberg and libretto by Sonenberg and Daniel Nester, made a strong impact, and it’s hard to tell whether this came from a compelling story or Sonenberg’s music or both.Highlights were a trio in which black baseball star Josh Gibson is cynically manipulated by two white baseball mavens and a lovely and moving aria by Gibson’s girlfriend. Performers were Michael Adams as Gibson, Zac Engle and Steven Eddy as the mavens, and Robie (a busy and valuable participant both Thursday and Friday) as the girlfriend.Carey was the pianist and Stephen Dubberly the conductor.“The Fox and the Pomegranate,” with music by Matt Frey and text by Daniel J. Kushner, is a strange parable featuring a “gender-fluid individual“ (Kushner’s words), dead animals, and exotic symbols (e.g., pomegranate juice to be smeared on faces).The text moves at a glacial pace, with much repetition of words including some held so long that it’s hard to grasp their meaning. The music, which is not unattractive, includes minimalist-like obsessions in the piano.This was only a sample of a work intended to be much longer. Maybe the full thing will offer some clarification.The biggest hit of the afternoon was clearly “Why I Live at the P.O.,” with music by Stephen Eddins and libretto by Michael O’Brien. This Welty-inspired comedy has a jazzy score (the familiar musical idiom may have been one factor in its popularity with the McDavid audience) and some clever situations that the cast brought off beautifully. The Frontiers works are not staged, but here was a chance for the cast to project some personality and talent for timing.All in all, Frontiers 2013 was a successful experiment and a nice break from standard operatic fare. Here’s to the 2014 version -- and maybe some excerpts beyond 20 minutes.