The Vowel Frequency Calculator tabulates the frequency with which each vowel occurs in a corpus.
The Vowel Co-occurence calculator looks at every pair of vowels in adjacent syllables (assuming no diphthongs), and tabulates co-occurence frequencies.
Results are given three vowel-pair matrices, one for all pairs in the corpus, one for first and second syllable pairs, and one for subsequent pairs (e.g., second and third syllabels, third and fourth, etc.