SWOT and STEEPLE are both techniques of analysis, used to judge the pros and cons of a business practice before placing it into motion.
SWOT stands for Strength, Weakness, Opportunity, and Threat, and is a generalized risk/benefit analysis used to examine the consequences of a business practice. The SWOT focus is on benefits and risks to the company, rather than to others.
STEEPLE (a variation on PEST analysis) stands for Social, Technological, Environmental, Economic, Political, Legal, and Ethical, and is a similar risk/benefit analysis, but with more detail and more focus on the long-reaching effects of the business practice rather than the internal benefits to the company.
Both methods are useful in different situations. For example, a privately-owned company might use SWOT over STEEPLE because they do not have to concern themselves with other factors, while a publicly-owned company would use STEEPLE to avoid problems with government and lobby groups. Either method should ultimately produce a practice that brings benefit to the company without harming or taking advantage of outside interests. Where impact on the company is of primary importance, the STEEPLE analysis allows a greater range of secondary impacts to be defined, while SWOT is faster and produces more generalized impacts. STEEPLE also allows the analysis to focus on specific parts -- a government bureau would focus on the Political aspect, while a private company would focus on Economic and Ethical.
The two models can also be used together; a STEEPLE analysis can identify many risk/benefit factors, which can then be generalized into a SWOT analysis for presentation.