Academic English 

Proficiency Exam Prep (University)
English Club           IELTS, TOEFL, TOEIC, Cambridge, Pearson, ++
EnglishTestStore     IELTS, TOEFL, TOEIC, SAT, GRE 
ExamEnglish          CEFR, TOEFL, IELTS, Cambridge, PTE, Trinity
BritishCouncil         IELTS, Aptis
PrepScholar           SAT, ACT, GRE, GMAT, PSAT, TOEFL
StudyIELTS            Australia Network IELTS Prep Video series (YouTube)

Oral Proficiency Exam (OPI) in English
ACTFL Tips            The test maker's basic info about test
My advice: 1) look at above site. 2) Find sites with "free sample Qs for the OPI" like Joseph YHC's or "free IELTS speaking practice questions" like IELTS Liz.  3) After you've practiced answers to common Qs on these sites, use AI as a chat partner. Here is a guide on what prompts & exercises to do: 

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YouTube
Scribbr                   How to on topics: Plagiarism, Lit Reviews, Citations, Dissertations, etc.
LundUni                 dozens of Eng videos, mostly about academic writing from Lund U, Sweden

Academic Writing Websites
Purdue Owl         Great resources for university writing
​UCalIrvine           Learn how to research, cite, & write papers
Phrasebank             U of Manchester. Great help w/ academic writing, organized by function. 

MOOCs Massive Open Online Courses 
U of Sydney Skills for University Success              a brilliant 5-module course 
US State Dept AE MOOCs                              for leaners & teachers 
Coursera                                                  list of popular MOOCs for EFL learners