Spine
Spine is built for games. You rig and animate characters, export data and atlases, and Spine runtimes play them in game engines. IK constraints, meshes and weights are in Spine Professional; Spine Essential does not include IK. Businesses with $500,000 or more in revenue need Spine Enterprise, licensed yearly.
Rive
Rive combines a vector editor, bones, meshes and an IK constraint with state machines and data binding. A character can look at the cursor, react to a tap or change mood with app data, all in the shipped file. Rive has a free plan (free exports show a splash screen) and paid plans from $9 per seat per month.
Moho
Moho is a character animation tool for video. It supports FK and IK, Smart Bones for clean joints and facial controls, and Bone Dynamics for follow-through. Moho Debut 14 costs $59.99 and Moho Pro 14 $399.99, both one-time.
Side by side
Output: Spine to game engines, Rive to app and web runtimes, Moho to rendered video. Interactivity: Rive is strongest; Spine relies on engine code; Moho has none at runtime. Price model: Spine and Moho one-time (Spine Enterprise yearly), Rive subscription with a free plan.
Our take
Making a game: Spine. Making an app or website mascot: Rive. Making an animated series or explainer videos: Moho. We make ExodeUI, which also has bones and IK and sits closest to Rive: characters in app UI, with open JSON files and AI tool support.