Two code base is completely different. HTM.core is a fork of NuPIC.core. And NuPIC.core was Numenta’s official implementation (no longer developed). While Etaler is a complete from scratch implementation.
To be clear. Both HTM.core and Etaler is a implementation of HTM (the theory and algorithm). But they are developed by different people and does not share a single line of code.
Edit: The code for my thread, Hierarchical Temporal Memory Agent in standard Reinforcement Learning Environment, uses Etaler as the base library to do HTM stuff.