The core requirement is to create custom applications for workflows like expense reports and time off, with a development team that has "only basic coding knowledge." This strongly points to a "no-code" or "low-code" platform.

AppSheet is Google's no-code development platform, designed specifically for users (often referred to as "citizen developers") with basic or no coding knowledge to build custom mobile and web applications directly from data sources like Google Sheets, Forms, or other databases. It's ideal for automating business processes and creating custom workflows without traditional programming.

Here's why the other options are less suitable:

A. Enable Gemini for Workspace. Direct users to use generative AI across Gmail and Drive to simplify the submission of expense reports. Gemini for Workspace (Google's AI assistant) can help with tasks like drafting emails, summarizing documents, and generating content within existing Workspace apps. While it can "simplify" aspects, it is not a platform for developing custom applications with structured workflows and data capture for tasks like full expense report submission or time-off requests. It enhances existing tools, it doesn't build new ones.

B. Direct employees to use Google Forms to collect data and create basic workflows. Google Forms is excellent for data collection and can be used for very simple workflows (e.g., collecting time-off requests). However, it lacks the robust functionality needed for complex custom applications, such as managing approvals, displaying data in different views, offline access, or integrating with other systems, without significant manual effort or custom scripting. The term "custom applications" suggests something more sophisticated than just a form.

D. Enable AppScript for your organization and allow employees to build add-ons to existing Workspace solutions. Google Apps Script allows for powerful automation and the creation of custom add-ons for Google Workspace applications (Gmail, Sheets, Docs). However, Apps Script requires knowledge of JavaScript. While it's relatively "basic coding" compared to full-stack development, it's still coding. The question emphasizes "only basic coding knowledge" and the need for a solution to develop applications, implying a more visual or declarative approach than coding from scratch. AppSheet is generally considered easier for those with "basic coding knowledge" or even no coding knowledge, making it a better fit for rapid application development by non-developers.

References from Google Workspace Administrator:

AppSheet: No-code App Development | Google Cloud: This is the primary resource for AppSheet, explicitly stating its purpose for "no-code app development" and enabling "everyone in your organization to build and extend applications without coding." It highlights use cases for automating business processes like order approvals (similar to expense reports/time off).