Dupe of #2055 but it's an open source 3DO emulator.
Mentioned on the Core-Requests page as well (at least one of them), even when others would still make a request.

Upstream info (4DO)

• Website
• Target platforms: win
• Source repo
• Language(s): C# (old .csproj format, but seems to target net40 and use WinForms+SlimDX for graphics)
• License: GNU GPLv2

Upstream info (Opera)

• Target platforms: win/mac/tux
• Source repo
• Language(s): C (libretro API)
• License: GNU GPLv2

Merits

Spike you just want this for Myst don't you?

No... Yeah.

Ok, but for real, after the addition of something like VirtualJaguar [CD] why not provide something that's got some things going for it as well and has more titles?
The 3DO did have different titles, and can possibly showcase some interest towards that system, much like how the Jaguar has not, but there is a long community that has jumped on the opportunity of having a new system in BizHawk to smash out some longplays even if the TASers don't capitalize on it.

Apologies. I don't actually have any technical details for this.
They both have save states to a degree depending on which one, they both have bios requirements, they both support disc swapping when required.