Actually it's OT on SO to ask for/recommend libraries, but I think the only open source choice is Pango:
Pango is a library for laying out and rendering of text, with an emphasis on internationalization."
[...]
Pango includes PangoLayout, a high level driver for laying out entire blocks of text, and routines to assist in editing internationalized text.
See the Script Gallery for a selection of European and other scripts that it can handle -- I don't see Hindi (Devanagari) or Tibetan, but it seems highly likely it has no problems with either.
Pango internally uses "Harfbuzz for complex-text handling". You could try both, and see how much work is required to get what you need using Harfbuzz alone, or go straight to Pango and get the all-inclusive package. (I wonder where to draw a dividing line in the functionality.)
FYI: part of the "advanced logic" that FreeType lacks can be attributed to handling OpenType positioning and glyph replacement. The FreeType developers appear to have concentrated primarily on drawing glyphs (see http://freetype.org/opentype/index.html), out-sourcing the logistics to Harfbuzz.