Also see here: https://www.optimizepress.com/blog/
they will very soon publish the new OptimizePress (so 5 years after OP2 I think - that was the version that first included Optimizemember aka s2member). I guess that's why 2018 saw nearly no activities on changelog. But OPM vs s2member changelog is virtually identical. They for sure tracked s2member via github or had some sort of agreement.
the differences between OPM and s2member are very very little. Worthy fix - they made it possible to send out register links without URL shortener (much better because those shorteners are often seen as spam). They added some sort of basic content dripping. Worthy misses - the CSS/JS optimization - plus it breaks pro-forms if you use autoptimize (they must have missed some s2member change here) - and not [s2_EOT] shortcode - however you can achieve much more via PHP (same goes for s2member though). I think they have 99 instead of 10 levels - but I don't need that. Well and the biggest difference is ThriveCart support - but I don't know if they ever did something for it - or if it was ThriveCart (excellent support and also very good coders!)
Well and of course support even though limited in scope vs no support at all with s2member. Support reacts pretty quick - but they are no coders. So basically they know ■■■■ about the advanced PHP possibilities of S2/OPM , they only know the basic stuff.
OptimizeMember 1.2.9 (8th March 2018)
Added full Google reCaptcha v2 support - as v1 will be deprecated soon
Fixed PayPal cancel button - to redirect to proper PayPal page
Translating Have a Coupon Code string
Fixed PayPal encryption in anchors and urls
OptimizePress 2.5.13 (8th March, 2018)
Fixed Media library edit image screen
Fixed overlay optimizer exit intent
Removed Hide YouTube logo from video player options (no longer supported by YouTube)
OptimizeLeads exclude pages
OptimizePress 18.104.22.168 (15th January, 2018)
Moved admin.js to the footer so we can dequeue it in OPPlus Pack if necessary
Fixed problems with Page Revisions on Edit Page screen
ActiveCampaign already subscribed bug fix
Fixed fullscreen bug for flowplayer on mobile devices
OptimizePress 22.214.171.124 (20th December, 2017)
Updated and improved fix for Chrome 63, to ensure Add Element in regular Posts and Pages works well
OptimizePress 126.96.36.199 (30th November 2017)
Added new GoToWebinar flow
Fix for the ActiveCampaign extra fields bug
Fixed a bug that caused Youtube video set to autoplay to start playing before OverlayOptimizer is opened
OptimizePress 2.5.12 (16th November 2017)
Fixed WP 4.9 issue
Disable fixed row on mobile option
Membership settings blank templates bug fix
Better error message display for OptimizeLeads WYSIWYG button
Enabling typography link/hover colour
Do notrender dashboard stats chart if there is no optin boxes data
Fixed fatal error in older PHP
OptimizePress 2.5.11 (4th October 2017)
OptimizeLeads button added to WYSIWYG WordPress editor
E-goi fix when using register() in optimizeMember Open registration option
Mailchimp resubscribe unsubscribed user throught optin form.
OptimizeLeads WYSIWYG editor button responsive design
Fix for php error: Can not use function return value in write context
Fixed a problem with Add Media button on WYSIWYG text elements in Firefox (the button was not working in some cases)
Do not define OptimizeLeads constants if they are already defined
Fixed post page when editing optin box textarea Form HTML (Custom Form) was empty.
Fixed conflicts between Optin Stats and WooCommerce plugin
Change active campaign api call contact_add to contact_sync when subscribing or registering user
Strip script tag from html string for Custom HTML element inside Live Editor.
Fixed a memory leak related to TinyMCE that caused browser to become unresponsive and crash after a longer usage
Fixed a notice that was happening on search pages
Removing Optimizepress Content Preview Page from WordPress search (op live search when you press enter)
Fix for tinymce is not defined JS error, when user disable the visual editor.
Custom optin form edit fix (illegal string offset content)
OptimizePress PlusPack 1.1.7 (4th October 2017)
Fixed Evergreen countdown timer cookie problems.
Fixed a problem with video background in Safari (autoplay for videos with sound is no longer allowed in new version of the browser)
Fixed Social sharing style3 to style7 to render Twitter icon properly
Syncing Optin Box in Plus Pack with OptimizePress
OptimizeMember 188.8.131.52 (18th July 2017)
Fix translation strings in login form element
PayPal IPN Compatibility: This release includes an updated PayPal IPN handler that is capable of reading number-suffixed IPN variables that are now being sent by PayPal’s IPN system in some cases, for some customers. We strongly encourage all site owners to upgrade to this release as soon as possible, particularly if they’re using PayPal to process transactions.
OptimizeMember 1.2.8 (19th June 2017)
PHP 7.1 compatibility
Fix for Stripe form in Facebook in-app browser