The atom editor is a free open source editor, that is easy to setup and use. It require two plugins to support processing sketches:-

1. script (the script plugin is capable of running processing.pde sketches and a large number of other scripts, including PiCrateand propane it supersedes the processing script by Bleikamp.
2. processing-language by Bleikamp

The script plugin assumes that you you have processing-java on your classpath on Debian linux you could use update-alternatives to provide a symbolic link, for other linux distros you could just use the ln -s command. On the Mac I believe there are instructions for installing processing-java from the ide see Bleikamp, which also describes how to add processing-java to the command prompt on Windows.

Much better editor options than with processing ide. I've also found that at least on linux I can replace the java in the processing ide, which seems to be blocked when using processing ide. I am currently experimenting with OpenJDK Runtime Environment GraalVM CE 21.1.0 (build 16.0.1+9-jvmci-21.1-b05) OpenJDK 64-Bit Server VM GraalVM CE 21.1.0 (build 16.0.1+9-jvmci-21.1-b05, mixed mode, sharing) with processing-4.0a3.