Well, there certainly are many legitimate tunings you can use, plus many more joke/anagram tunings.

No one seems to have mentioned the two most basic tunings for American folk/blues guitar, both of which can be achieved in either of two different keys. So, let's review:

"Spanish": from standard tuning, you can either tune the D/G/B strings UP to open A, or the (low)E/A/(high)E strings DOWN to open G.

"Vastapol: again starting from standard tuning, the alternatives are stretching the A/D/G strings UP to open E or loosening the G/B/(high)E DOWN to open D.

Electric blues players tend to favor open E and open A, probably because their extra-light strings and heavy-duty instrument bodies can stand the strain (and also, probabaly, because when they play in bands with guitars and basses in standard tuning, E and A are "better" keys for playing blues).

Acoustic players are more likely to tune down to open-D VAstapol and open-G Spanish.

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On the subject of partial-capoing: I've become "partial" (pun intended) to capoing the five top strings at the second fret to simulate dropped-D tuning (playing in E, actually). This allows me to use standard chord shapes including the bottom string whenever the bottom string is fretted at the 4th fret or above. I don't hve the time or energy to explain from the get-go, but those who understand the logic behind the partial capo will know what I've talking about.