There are multiple good mathematics courses to take online, including courses provided by Alison and MIT Open Courseware. Many of the mathematics courses available online offer students a certificate upon completion.
The online courses available from Alison include a Diploma in Mathematics course, a Diploma in Statistics course, a Foundation Diploma in Mathematics and more. All these courses are free, and their durations are approximately 10 hours. MIT Open Courseware offers mathematics courses and qualifications at undergraduate and postgraduate levels. Some of the courses provided include Single Variable Calculus, Linear Algebra, Mathematics for Computer Science and Introduction to Functional Analysis.