I know of 3 good tools with a MonoGame runtime that can help you with 2d skeletal animation.
- Spine is probably the most polished tool out there. It does not have a free version, the ‘essential’ version ($70) does not support inverse kinematics or mesh deformation (deforming sprites during an animation). The ‘professional’ version is $300 or something. It has an official MonoGame runtime on the following page: https://github.com/EsotericSoftware/spine-runtimes
- An alternative with a free version is Spriter. Free version does not support advanced kinematics, mesh deformation, advanced tweeting curves and triggers (events during animation). Full version is $60. The MonoGame runtime is on GitHub at https://github.com/loodakrawa/SpriterDotNet
- DragonBones is a completely free tool with some of the features that are only in the paid versions in Spriter and Spine, like inverse kinematics, mesh deformation and events. The creators provide a C# runtime and @caotrong got it working with MonoGame.
You could of course roll your own tool and runtime, like the peeps that made Salt & Sanctuary: http://www.gdcvault.com/play/1024155/Postmortem-Salt-and-Sanctuary