I'd say Google Analytics
Merchant accounts for processing payments
Email marketing software
Anti-virus and data storage
In today's day and age I feel that mobile applications are a must have.
This may vary from business to business. But here are the ones I'd recommend.
1. Great domain - needs to be catchy and resonate well with your target audience
2. Affordable hosting - important
3. Marketing tools
4. Payment processing software
5. Accounting software
Chatbots are a great thing for CRM software. They are available 24/7 and can interact simultaneously with a thousand users.
Good backup storage space is a must nowadays.
Also, I can't stress enough, you do need lot of IT experts for your computers. IT division is a must now.
Pretty good points have been raised here.
But I'll say for any business to thrive especially small business. The following technologies will be needed.
1. Fast computers/ laptop
2. payment processor
3. Hand-held device (smartphones)
4. accounting software
5. Data storage capabilities