This type of software testing is very informal and unstructured and can be performed by any stakeholder with no reference to any test case or test design documents. The person performing Ad-hoc testing has a good understanding of the domain and workflows of the application to try to find defects and break the software.
Wolfram Alpha is a computational search engine (sometimes referred to as an answer engine). The interface looks similar to that of a regular search engine but queries typed into the search box result answers to specific questions rather than listings of websites that may be relevant to the query.
Online Integral Calculator. More than just an online integral solver. Wolfram|Alpha is a great tool for calculating antiderivatives and definite integrals, double and triple integrals, and improper integrals. It also shows plots, alternate forms, and other relevant information to enhance your mathematical intuition.