Replacing allocators https://github.com/jemalloc/jemalloc/wiki/Getting-Started

Pretending you're running on a remote system https://github.com/viraptor/libremotec

Cheat in games https://github.com/ProfessionallyEvil/LD_PRELOAD-rand-Hijack...

Fixing bugs where the upstream can't do it.

Some uses of LD_PRELOAD off the top of my head:

- GNU stdbuf (BSDs use an env-var instead of hijacking libc)

- fakeroot

- gprofng's data collector

- For a long time it was necessary to use LD_PRELOADto hack around a bug in flashplayer because flashplayer used memcpy when it should have used memmove.

Do you mean the functionality itself (inherent in the capabilities of a dynamic ELF loader) or specifically that it uses an environment variable? Maybe moving it to static configuration in ld.so.conf would cut down on abuse.

tsocks is quite useful for proxying a program's network access over ssh using SOCKS. I use it for accessing geo-blocked servers using command line tools without a full VPN.

Fixing bugs in a function in a library. Overriding libraries.