HTTPulse is described as 'Zero-setup, browser based solution for performing REST API health checks and load tests'. There are more than 25 alternatives to HTTPulse, not only websites but also apps for a variety of platforms, including Windows, Linux, Mac and Self-Hosted solutions. The best alternative is Apache JMeter, which is both free and Open Source. Other great sites and apps similar to HTTPulse are locust (Free, Open Source), hey (Free, Open Source), Loader.io (Freemium) and Tsung (Free, Open Source).
Apache JMeter is an open source Java application, designed to load test functional behavior and measure performance. Originally designed for testing Web Applications, it has since expanded to other test functions as well.
Tsung (formerly IDX-Tsunami) is a distributed load testing tool. It is protocol-independent and can currently be used to stress HTTP, WebDAV, SOAP, PostgreSQL, MySQL, LDAP and Jabber/XMPP servers. It is distributed under the GNU General Public License version 2.
ab is a tool for benchmarking your web server. It is designed to give you an impression of how your current web server installation performs. This especially shows you how many requests per second your web server installation is capable of serving.