[gruturo]

Yep it's full of IP protocols other than the well-known TCP, UDP and ICMP (and, if you ever had the displeasure of learning IPSEC, its AH and ESP).

A bunch of multicast stuff (IGMP, PIM)

A few routing protocols (OSPF, but notably not BGP which just uses TCP, and (usually) not MPLS which just goes over the wire - it sits at the same layer as IP and not above it)

A few VPN/encapsulation solutions like GRE, IP-in-IP, L2TP and probably others I can't remember

As usual, Wikipedia has got you covered, much better than my own recollection: https://en.wikipedia.org/wiki/List_of_IP_protocol_numbers

[lxgr]

To GPs point, though, most of these will unfortunately be dropped by most middleboxes for various reasons.

Behind a NA(P)T, you can obviously only use those protocols that the translator knows how to remap ports for.

[Hikikomori]

Can also do 1:1 NAT for IP protocols like ipsec, or your own protocol.