Porting applications to computing platforms is a costly and error-prone process which is often replicated several times while sharing applications would enable repurposing and facilitate interoperability. Existing application-sharing systems are usually bound to a particular infrastructure or execution environment, which makes applications hardly transferable between platforms. Recently, the wide spreading of Linux containerization, in particular through the Docker system, has enabled the sharing of virtual appliances at an unprecedented scale. We present the Boutiques application-sharing system based on Docker containers. Applications described in Boutiques consist of (1) a JSON descriptor stored in a Git repository and (2) a Docker image containing the application and all its dependencies. We implemented software tools to create Boutiques applications and to import them to CBRAIN [1], VIP [2], and Pegasus [3]. Using this framework, we were able to import 11 applications from Boutiques to our three platforms in a few hours only. This proves the concept of Boutiques which we plan to extend to other computing platforms and to more complex application descriptions, including pipelines.