It worked for me once. I was helping someone to configure their new FritzBox router(*) and among other things I briefly tested VPN. They don't make it easy to use with something else, at first sight it's not even apparent that it's IPSec, they have own Windows client, some "magic" program for creating configuration, and they don't show any technical details anywhere (I hope I'm not being unfair, I didn't have too much time to play with it). Anyway, after some trial and error, I was able to connect to that from RouterOS. I can't test it anymore, but these are leftovers from that experiment from my test router:
/ip ipsec peer
add address=<fritz IP> auth-method=pre-shared-key-xauth dh-group=modp1024 enc-algorithm=aes-256 \
exchange-mode=aggressive generate-policy=port-strict mode-config=request-only my-id=key-id:admin \
secret=<secret> xauth-login=admin xauth-password=<password>
/ip ipsec policy
add dst-address=192.168.10.0/24 sa-dst-address=<fritz IP> sa-src-address=<my IP> src-address=\
192.168.10.0/24 tunnel=yes
No guarantees, but it worked once (and I didn't try again).
(*) The whole experience was horrible. I guess they want to be user friendly, but I couldn't configure almost anything. Second IP address, impossible. Forwarded port limited to selected source addresses, impossible. And everything was sooooo convoluted. Since then, I like RouterOS even more than I did before.