List of third party programs

http://boards.na.leagueoflegends.com/en/c/player-behavior-moderation/5dmkJinG-3rd-party-applicationsmodifications-whats-allowed-and-what-isnt

all third party programs are technically "use at your own risk"

there's definitely some that are forbidden, like ones that make any alterations to ingame files or provide any, even miniscule, gameplay advantage for yourself or provides info that should otherwise not be provided to you. also custom skins that are copies of existing Riot skins are not allowed but they do not mind original, player-made skins that are completely different than riot official skins, though that said the third party progrms for custom skins are also use-at-own-risk since you never know EXACTLY how they're working, what they're changing, or if there are any "other" features that their detection will mark as malicious.

for a more detailed and official read, do check out this link: https://support.riotgames.com/hc/en-us/articles/225266848