Below are a variety of tools and information in the Wormhole ecosystem that can help you develop xDapps.
Wormhole's component design specifications outline the reasoning behind design decisions with added technical depth.
Wormhole has deployed Core Bridge, Token Bridge and NFT Bridge contracts on various testnets of the chains connected by Wormhole. You can see the deployed addresses here.
Note: There's only a single Guardian that oversees the testnets, so you might experience a higher rate of missed VAAs than you would on mainnet.
An example UI provided to test out attesting and bridging tokens on testnet.
Tilt is a Kubernetes-based tool that runs a copy of every chain along side a Guardian node to create a simulated testing environment. Details on how to set it up and test against it is here.
The Wormhole core repository can be found at https://github.com/wormhole-foundation/wormhole.
Tool to observe all Wormhole activity and can help you parse VAAs after they've been picked up the Guardian network.