I need a self-contained program that plans and tracks yearly maintenance for my gas detection sensors. Each client can have anything from a single service visit up to 12 per year, covering 1–75 sensors at a time. Core workflow I want: • Automatic scheduling – as soon as I enter a new client or finish a visit, the system should calculate the next maintenance period and place it on a calendar. • Contact management – names, phone numbers and emails are stored directly in the program so I can reach the right person every time. • Eight-week reminders – the system sends an email exactly eight weeks before the visit, prompting me to order spare parts. • Spare-part traceability – when I register parts I must capture serial number and best-before date; this information should be visible at that same eight-week mark so ordering decisions are easy. • Appointment handling – from inside the program I can propose a date, the client clicks to confirm, and both sides get a confirmation email. • Invoicing choice – I decide per job whether to bill against a pre-supplied order number or send a pro-forma invoice after the work is done. • Custom reporting – exportable summaries of upcoming jobs, parts used, and invoicing status. I’m happy with a straightforward, desktop or web-based solution; use the tools and language you’re most comfortable with as long as the interface stays clean and future tweaks are possible. Deliverables: a functional prototype that covers every point above, installation/setup instructions, and brief user notes. If the collaboration goes smoothly, I will commission extra features in a follow-up phase.