Generally speaking, Ringba does not have a marketplace app framework. However, Ringba is 100% API-based, which means providers can build applications that work with Ringba using nothing more than an API access token.
Ringba does not provide sandbox, testing, or temporary environments to support these efforts, but you can use a regular production account:
If you are a Ringba user with a provider who wants to help you integrate their product with your Ringba account, your admin user can generate an API access token to share with your partner so they can get the integration working for you.
If you are the provider creating an integration to offer to clients and prospects, you should sign up for your own Ringba account with the appropriate subscription plan: most likely the Professional plan, but you might need to upgrade to Enterprise if your integration involves real-time bidding. After you have built your integration and published the custom application to your marketplace, Ringba will offer a 100% refund of the subscription costs involved in building the integration.
You can check out Ringba's Developer Documentation for instructions on using the available endpoints.