My MIT-licensed high-performance rust rewrite of tac has just been updated to version 2.0. The announcement blog post talks about what it took to add AVX2 acceleration to the rust code and some issues I ran into with the llvm codegen backend when using compiler intrinsics to speed things up and how I worked around them.
This release of tac is 3x faster than the GNU Coreutils version of tac (which makes a big difference if you're using it as part of the toolchain to process 100 GiB+ log files). Pre-compiled binaries are available for major platforms. Help is requested in getting it into the various package managers, though! There's a discussion post on Hacker News and on r/rust if you want to join in the fun.