PaaS (Platform as a service) systems are revolutionizing the way modern applications are developed and hosted. Current PaaS offerings provide limited support for managing SLAs (Service Level Agreements) that constrain application quality properties, such as response times. To overcome this limitation, PaaS systems should be capable of dynamically adjusting resource allocations to meet provider objectives. At the same time, PaaS systems should retain their extensibility to host diverse application types. In this paper we propose Meryn, an open, SLA-driven, PaaS system that aims at maximizing the provider profit and providing SLA guarantees to diverse application types. Meryn provides support for cloud bursting and applies a decentralized protocol for selecting resources to run applications. This protocol tries to minimize the cost of running applications without affecting their agreed quality properties. We implemented a prototype of the Meryn system and performed a preliminary evaluation. The results show that the effectiveness of Meryn in optimizing the provider profit is very promising.