There are several tools for indexing:
- luaindex (one release from 2011, written in Lua, "This is an alpha version!", by Markus Kohm)
- makeindex (1987-1993, written in C, by L. Lamport, P. Chen et al.)
- xindy (last release 2013, written in CLISP, by J. Schrod)
- xindex (several releases in 2019, written in Lua, UTF-8 support but compatible with makeindex, by Herbert Voß)
- and many more
What should a user keep in mind when selecting the right index tool for an UTF-8 lualatex document in 2019?