Generating messages having in-message applications

A method comprising:

• receiving a first message at a system comprising multiple client computing devices each storing one or more application identifiers, templates, and client software, wherein the templates each define respective visual structures for in-message applications, and wherein the client software stored on each client computing device is operable, when executed by the client computing device, to receive a message that contains message content and a reference identifying a location of external data, and to render on the client computing device an in-message application specified by an application identifier in the external data, external content in the external data, the message content, and one or more mappings according to the visual structure defined by a respective template for the in-message application specified by the application identifier, wherein the first message contains first message content and a first reference identifying a location of first external data, wherein the location is a location on an external data provider and the first external data is accessible through the first reference;
• obtaining, through the first reference, the first external data, wherein the first external data includes (i) a first application identifier that identifies a first in-message application that has a user interface (UI) component, (ii) first external content, and (iii) one or more first mappings of elements of the first external content to the UI component;
• generating a second message that includes the first message content, the first application identifier, the first external content, and the one or more first mappings;
• and
• broadcasting the second message to respective client software of one or more client computing devices of the multiple client computing devices.

One or more non-transitory computer-readable storage media encoded with instructions that are operable, when executed by one or more server computers on a system, to cause the one or more server computers that implements a real-time messaging platform to perform operations comprising:

• receiving a first message at a system comprising multiple client computing devices each storing one or more application identifiers, templates, and client software, wherein the templates each define respective visual structures for in-message applications, and wherein the client software stored on each client computing device is operable, when executed by the client computing device, to receive a message that contains message content and a reference identifying a location of external data, and to render on the client computing device an in-message application specified by an application identifier in the external data, external content in the external data, the message content, and one or more mappings according to the visual structure defined by a respective template for the in-message application specified by the application identifier, wherein the first message contains first message content and a first reference identifying a location of first external data, wherein the location is a location on an external data provider and the first external data is accessible through the first reference;
• obtaining, through the first reference, the first external data, wherein the first external data includes (i) a first application identifier that identifies a first in-message application that has a user interface (UI) component, (ii) first external content, and (iii) one or more first mappings of elements of the first external content to the UI component;
• generating a second message that includes the first message content, the first application identifier, the first external content, and the one or more first mappings;
• and
• broadcasting the second message to respective client software of one or more client computing devices of the multiple client computing devices.