We are planning to increase/improve on the the library of available pre-set alternate tuning, but meanwhile feel free to create your own custom tunings. Here are some of the common alternate tunings that are not pre-set:
Full step down : D2 - G2 - C3 - F3 - A3 - D4
Drop C: C2 - G2 - C3 - F3 - A3 - D4
Drop C#: C2♯ - G2♯ - C3♯ - F3# - A3♯ - D4♯
Half step down: E2b - G2♯ - C3♯ - F3♯ - B3b - E4b (same like Eb tuning)
Open E: E2 - B2 - E3 - G3♯ - B3 - E4
Drop B: B1 - F2♯ - B2 - E3 - G3♯ - C4♯
Drop A 7-string: A1 - E2 - A2 - D3 - G3 - B3 - E4
Drop A 6-string: A1 - E2 - A2 - D3 - F3♯ - B3
If you want to find out more about the scientific pitch notation (the numbers next to the note) please check this article.