Maverick Model 3D is a 3D model editor that supports skeletal and vertex frame animations. It is based on Misfit Model 3D that was developed by Kevin Worcester from 2004 to 2009. I maintain Maverick Model 3D.
Maverick Model 3D fixes various issues, improves MD3 model support (including fixing normals in exported player upper.md3 and head.md3), adds support for saving IQE models, improves Windows and macOS support, and uses Qt 5.x.
I would recommend trying Maverick Model 3D if you currently use Misfit Model 3D for creating MD3 models for Quake 3. IQE (a skeletal model format) can be converted to IQM format using the iqm program in the IQM development kit. IQM format can be loaded by ioquake3 (but can’t replace existing MD3 models so it’s mainly useful for mods or standalone games).
You can download it for Windows and macOS at the Maverick Model 3D website. The GPLv2+ source code is available which also builds and runs on GNU/Linux.