Inventory management:

Product database: The app needs to have a comprehensive product database where all the products can be added along with key details like product name, description, category, barcode/SKU, manufacturer details, specifications, images etc. This acts as the backend for all inventory related operations.

Stock tracking: The app should allow adding the stock quantity for each product. It should also allow editing the stock level as products are sold or received. Having an integrated barcode/RFID scanner makes stock tracking much faster.

Reorder alerts: Setting minimum stock levels and being alerted via notifications when products drop below those minimum levels ensures timely reorders.

Batch/serial tracking: For products that require batch or serial numbers like electronics or pharmaceuticals, the app should allow adding those details for better traceability.

Multiple storage locations: For businesses with multiple warehouses/stores, the inventory can be tracked by location for better visibility. Products can be transferred between locations.

Bulk product editing: Features like mass updating prices, changing categories/specs in bulk improves efficiency while managing a large product catalog.

Expiry/warranty tracking: Tracking expiry and warranty dates is important for perishable or installed base products. The app should allow adding these fields and notifications.

Vendors/Supplier management: The suppliers for each product need to be tracked. Payment history, price quotes, order cycles etc need to integrated for purchase management.

BOM/Kitting management: For products assembled from other components, the app should support Bill of Materials, exploded views of components, kitting/packaging of finished goods.

Sales & Order management:

Sales order entry: Allow adding new sales orders/invoices on the go. Capture customer, billing/shipping address, payment terms, product details etc.

POS mode: A lightweight POS mode for quick order entry, payment capture while customers wait at a retail store counter. Integrates directly with inventory.

Shipments/Fulfillment: Upon order confirmation, the app should guide pick-pack-ship tasks and automatically update inventory and order status.

Returns/Credits: Features to process returns, track return reasons, issue credits against invoices and restock returned inventory.

Layaways/Backorders: For products not currently available, the app must support partial payments, fulfillment tracking as stock comes in.

Quotes to orders conversion: Convert customer quotes to binding sales orders with one click when they are ready to purchase.

Recurring orders: Set up recurring/subscription orders that replenish automatically on defined schedules.

Invoicing/Receipts: Customizable invoice templates. Email or print invoices/receipts from the mobile device.

Payment tracking: Support multiple payment methods – cash, checks, cards or online payments. Track payment status.

Customers/Contacts database: Capture all customer master data – profiles, addresses, payment terms, purchase history, customized pricing etc.

Reports: Dozens of pre-built reports on KPIs like top selling products, profitability by customer, inventory aging etc. Generate as PDFs.

Notifications: Timely notifications to team members for tasks like low inventory, expiring products, upcoming shipments, payments due etc.

Calendar view: A shared calendar view of all sales orders, shipments, invoices, payments and their due dates for better coordination.

Team roles: Define roles like manager, salesperson, warehouse staff with customizable permissions to access features.

Offline use: The app should work offline when connectivity is unavailable and synchronize seamlessly once back online.

For building a truly unified, AI-powered solution, some additional capabilities could include-

Predictive analytics: AI-driven forecasting of demand, sales, inventory levels based on past data to optimize operations.

Computer vision: Leverage mobile cameras for applications like automated inventory audits, damage detection, issue diagnosis using computer vision & machine learning models.

AR/VR: Use augmented reality for applications like remote support, virtual product demonstrations, online trade shows, 3D configurators to enhance customer experience.

Custom fields: Ability to add custom multi-select fields, attributes to track additional product/customer properties like colors, materials, customer interests etc. for better segmentation.

Blockchain integration: Leverage blockchain for traceability, anti-counterfeiting uses cases like tracking minerals, authenticating high-value goods across the supply chain with transparency.

Dashboards/KPIs: Role-based customizable analytics dashboard available on all devices with real-time health stats of business, trigger-based alerts for anomalies.

Those cover the key functional requirements to develop a comprehensive yet easy to use mobile inventory and sales management solution for businesses of all sizes to gain transparency, efficiencies and growth opportunities through digital transformation. The extensibility helps future-proof the investment as needs evolve with mobile-first capabilities.