Due to a recent change by overwolf and a number of duplicate posts I've gone ahead and made a MEGATHREAD (read in quake announcer voice) for the topic. All new posts on the topic will be removed and you are encouraged to discuss the changes here. Links to the original posts:

https://www.reddit.com/r/feedthebeast/comments/k1kd53/psa_avoid_overwolf_software_with_alternative/

Currently there are 2 good options available. Both allow instances (separate version and modpack installations that do not interfere with eachother). Both allow granular mod enabling/disabling as well as drag drop mod jar installation.

GDLauncher https://gdevs.io/ - This launcher can download modpacks and mods direct from curseforge and allows upgrades in-place, similar to the old twich app.

MultiMC https://multimc.org/ - This launcher can download modpacks directly from curseforge, and FTB (yay exclusives), as well as Technic. You will need to be on the development update channel (in settings, change Stable to Development). per /u/robotic_rodent_007

you can tell MultiMC to use your existing twitch folders by following this post: here

Neither of these require Overwolf software, and both are good choices. You only need one, not both.

edit: ATLauncher https://atlauncher.com/ is also a valid choice which can download Curseforge modpacks (thanks u/TheSaucyWelshman) and has its own selection of modpacks that may not be available on other platforms .

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edit 2: after some concerns were messaged to me, i figured it would be a good opportunity to share why FTB made this move, why they are including ads in their app, and some of their future plans:

https://forum.feed-the-beast.com/threads/ftb-curseforge-overwolf-and-the-future.303428/

While I appreciate their motive, I disagree with their direction and will be sticking to alternative launchers for now.

https://www.reddit.com/r/feedthebeast/comments/k1jaak/overwolf_launcher_game_doesnt_work/

I was playing Revelations this morning no problem. Went to launch FTBapp from my start menu and it made me install Overwolf? Now when I click play on the Minecraft launcher Java runs but I get no screen. This happening to anyone else?

https://www.reddit.com/r/feedthebeast/comments/k1iya1/click_the_ftb_shortcut_today_and_it_makes_me/

I have had overwolf before and really didnt like it. I then opened the ftb app through the folder and it worked fine?

https://www.reddit.com/r/feedthebeast/comments/k1imi1/question_regarding_curseforge_overwolf_twitch/

So I haven't played in a bit, but I do still have some saves of Minecraft on the Twitch launcher with some packs, so today I updated my twitch launcher again, updated some packs, cause I might play again. But there is a message regarding that there is a new home for 'Curseforge'. So how does this work, do I install overwolf and that's it, or do I have to migrate what I have towards Overwolf, if so how etc ?