Sometimes there may be things your client needs that are not supported in StickyApps.  Here are some options available to you.

Calendars:

Google Calendar - Free resource and can be updated easily by your clients as new events are scheduled.

Scheduling:

Calendly App: Syncs with Google Calendar and offers both a free and paid option.

Set More - Online booking tool offers both a free version and additional feautres with a premium paid version.

FIle hosting (PDF/Word/Audio)

Dropbox  Has both free and paid for small files (word documents) is a great option, Note: Link directly to the file (not a folder) in Dropbox.

Google Documents  Free online tool for creating documents, do need to have a Gmail account.  In addition to creating documents  can upload files, such as video, audio and PDF files to share. 

Forms:
TypeForm - Online for creation tool, for forms/data collection.  There is a free and a paid version. 

Google Forms - Free online resource to create forms, data saved to the clients Google Drive account.

Shopping Cart:

Shopify - Paid services with several price options. Your clients and manage and maintain as inventory moves quickly

Etsy  Option for artists and creatives, allows them to make updates as they have new products.

Amazon Option for companies who want a bigger web presence

Payment Options (one time or reocurring)

PayPal - Allows you to take one time payments or set up recurring payments using the paypal platform.  There is an additional fee to do this through their service.

Moonclerk - Service that uses Stripe and take payments (one time) or reoccurring. The cost is a small fee to use the service, plus Stripe fees.

Plasso - Service offers reoccurring and one time payments, invoices and pre-orders.  Fees vary based upon plan, and do not include Stripe fees. Note: Free plan allows for up to 15 transactions a month (before you pay).