"What is an alternative to Salesforce?"
Consider understanding what advantages are associated with Salesforce as a tool first. From there, you can objectively evaluate the relevance of those advantages for your situation.
Take a look at this list of Salesforce advantages and then assess their relevancy for you:
1) You have separate marketing and sales teams
2) You have or plan to launch marketing automation where dynamic behavioral targeting is an effective part of the strategy (Marketo, Pardot, Intercom, MaroPost are all tools that enable this)
3) Your offering involves a complex sales cycle
4) Cross-departmental integration beyond sales and marketing is desired
So the circumstances involve either no sales teams, no complex sales cycle or massive integration. Here are some options that meet those criteria:
For the solopreneur:
17 Hats - This provides a CRM, lead capture pages that are customizable, workflow automation, contact book, and integrates with your email, your bank account and your calendar. Pricing at either: $29/mth, $17/mth (annual or $13/mth (bi-annual)
For the massive integration:
Netsuite - Netsuite is what is called an ERP system. While the sales side is not as nice as Salesforce, it offers better integration from a customer / technical support / accounting perspective. Pricing starts at around: $100/mth per user
InfusionSoft, SugarCRM and Zoho CRMS - I don't like or recommend these services. I have used them and the lack of control to manipulate the data just won't do. The point of a CRM is data centralization. The existence of data centralization, to drive informed decision making in sales and marketing. I have not found these CRMs to properly build in reporting that easily and comprehensively correlates data to drive informed decision making. Salesforce provides the customization to correlate data as you see fit. These reasons contribute to why Salesforce remains considered best of breed among CRMs.