Spaced repetition systems have gotten better

Anki is a good piece of software. But I couldn't come up with a worse scheduling algorithm if I tried (old and new one). It's like "here's the thing you just added one second ago. Here it's again immediately after. Ok you got it, you'll see it once again in a month or so lol".

It makes it unusable and every time I tried I went back to my own self written program that just lets me set/adjust the intervals myself.

When was the last time you tried? Anki used a static algorithm (SuperMemo 2) before the new FSRS - which is dramatically different.

In the short term (first day), I think it's still better to set your own intervals (typicall 1 minute, then 5, then 10). But after that, the algorithm optimizes for reminding you just before forgetting. Highly recommend giving it a try.

I try Anki every couple of years because it has an app and can sync. I also tried fsrs and rage quitted after a few tests. These people can get high and mighty on their algos and research. If they'd just add a manual interval mode they'd contribute a lot more to humanity.

I guess what you need is Set Due Date, which allows you manually schedule cards in Anki.

In my own tool I can do "+10%" or "+2 days"

Good feature! I guess someone could implement it via an add-on of Anki.