[Tiberium]

Telegram's Saved Messages (essentially self-texting) is also commonly used for saving info, somewhat recently they even added tagging and the ability to view messages that you forwarded into there per chat (so you can see all messages that you ever saved from some group you're in). Of course it all lives on their cloud and is not local.

[bayesianbot]

Though tagging is only available for the (kinda pricey) Premium subscription.

[eguchi1904]

Tagging is actually available for free, so just wanted to correct that.

[bayesianbot]

Huh? I just tried tagging a message, which opens a popup for Telegram Premium. Also web search brings up "Tags are already available to all Telegram Premium users." from Telegram website - it's an old post, but I don't see anything anywhere that says otherwise. Or do you mean #hashtags?

[naught0]

They're (OP) almost definitely referring to their own service which has tagging built in for free.

[eguchi1904]

oh, you were talking about Telegram. I misunderstood it. My bad.