I could only get it to work in read-only mode though. The software you'll need to install are, in this order:
- OSXFUSE (2.6.0 at time of writing). This is the successor to MacFUSE, which is no longer maintained and should be considered outdated. Make sure to install the MacFUSE compatibility layer when installing OSXFUSE (you may have to choose this explicitly under custom install within the installer).
- Fuse-ext2 (0.0.7 at time of writing). More Fuse-ext2 documentation is available.
I could not get it to mount in read and write mode.
Note that if you format the drive in GParted - Gnome Partition Editor, it may inadvertently partition it in some Linux format that Macs cannot read at all (Mac OS X will prompt you to initialize the drive, thus erasing all data). I used GNOME Disks to format just the volume to Ext2/3/4, without erasing and re-partitioning the disk.
In my opinion, the state of affairs of disk formats is really quite sad when it comes to cross-platform interoperability. There is no easy to use, reliable, and modern file system that is full featured on all three major platforms: Windows, Mac, and Linux. The closest is FAT file system, which is decidedly not modern.