You're right, Ian; even without the slide (which is the ultimate "crutch" for eliminating strain on the left-hand fingers), alternate and open tunings often create opprtunities to play with fewer fingers and easier fingerings than standard.

I can play a few basic slide-blues riffs in open G and open D (or E), just enough to bore myself to death through a few repetitive choruses of basic 12-bar blues.

Beyond that, I have a "repertoire" of exactly three songs in open D, each with a very different "sound" from the other two, and only one of them utilizing the slide. They are, all three, much easiler on the left hand than most anything I play in standard:

~ Mississippi John Hurt's "Payday," a blues-ish country folksong that is not "Delta" style, not played with the slide, and not in 12-bar format.

~ The Paul Brady arrangement of "Lakes of Pontchartrain," which has a sort of "DADGAD-like" Celtic sound. (I'm still having trouble playing and singing this at the same time. Brady capos up four frets; I have trouble vocalizing the high notes even with no capo at all.)

~ A slide-guitar version of the old spiritual "Twelve Gates to the City" that I learned from the great master Fred MacDowell way back when I had the opportunity to meet him back in 1968. It's not in 12-bar form, and is definitely not "devil's music" blues, but it shares a very sharp and eerie sound with the bluest of hard-core Delta blues.